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# 2. 自定义扩展类型：教程
Python 允许编写 C 扩展模块定义可以从 Python 代码中操纵的新类型，这很像内置的 [`str`](../library/stdtypes.xhtml#str "str") 和 [`list`](../library/stdtypes.xhtml#list "list") 类型。所有扩展类型的代码都遵循一个模式，但是在您开始之前，您需要了解一些细节。这份文件是对这个主题介绍。
## 2.1. 基础
[CPython](../glossary.xhtml#term-cpython) 运行时将所有 Python 对象都视为类型 [`PyObject*`](../c-api/structures.xhtml#c.PyObject "PyObject") 的变量，即所有 Python 对象的"基础类型"。 [`PyObject`](../c-api/structures.xhtml#c.PyObject "PyObject") 结构体本身包含了对象的 [reference count](../glossary.xhtml#term-reference-count) 和对象的"类型对象"。 类型对象确定解释器需要调用哪些 (C) 函数，例如一个属性查询一个对象，一个方法调用，或者与另一个对象相乘。 这些 C 函数被称为“类型方法”。
所以，如果你想要定义新的扩展类型，需要创建新的类型对象。
这类事情只能用例子解释，这里用一个最小化但完整的的模块，定义了新的类型叫做 `Custom` 在C扩展模块 `custom` 里。
注解
这里展示的方法是定义 *static* 扩展类型的传统方法。可以适合大部分用途。C API也可以定义在堆上分配的扩展类型，使用 [`PyType_FromSpec()`](../c-api/type.xhtml#c.PyType_FromSpec "PyType_FromSpec") 函数，但不在本入门里讨论。
```
#define PY_SSIZE_T_CLEAN
#include <Python.h>
typedef struct {
PyObject_HEAD
/* Type-specific fields go here. */
} CustomObject;
static PyTypeObject CustomType = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "custom.Custom",
.tp_doc = "Custom objects",
.tp_basicsize = sizeof(CustomObject),
.tp_itemsize = 0,
.tp_flags = Py_TPFLAGS_DEFAULT,
.tp_new = PyType_GenericNew,
};
static PyModuleDef custommodule = {
PyModuleDef_HEAD_INIT,
.m_name = "custom",
.m_doc = "Example module that creates an extension type.",
.m_size = -1,
};
PyMODINIT_FUNC
PyInit_custom(void)
{
PyObject *m;
if (PyType_Ready(&CustomType) < 0)
return NULL;
m = PyModule_Create(&custommodule);
if (m == NULL)
return NULL;
Py_INCREF(&CustomType);
PyModule_AddObject(m, "Custom", (PyObject *) &CustomType);
return m;
}
```
这部分很容易理解，这是为了跟上一章能对接上。这个文件定义了三件事：
1. `Custom` 类的对象 **object** 包含了： `CustomObject` 结构，这会为每个 `Custom` 实例分配一次。
2. `Custom` **type** 的行为：这是 `CustomType` 结构体，其定义了一堆标识和函数指针，会指向解释器里请求的操作。
3. 初始化 `custom` 模块： `PyInit_custom` 函数和对应的 `custommodule` 结构体。
结构的第一块是
```
typedef struct {
PyObject_HEAD
} CustomObject;
```
This is what a Custom object will contain. `PyObject_HEAD` is mandatory at the start of each object struct and defines a field called `ob_base`of type [`PyObject`](../c-api/structures.xhtml#c.PyObject "PyObject"), containing a pointer to a type object and a reference count (these can be accessed using the macros [`Py_REFCNT`](../c-api/structures.xhtml#c.Py_REFCNT "Py_REFCNT")and [`Py_TYPE`](../c-api/structures.xhtml#c.Py_TYPE "Py_TYPE") respectively). The reason for the macro is to abstract away the layout and to enable additional fields in debug builds.
注解
There is no semicolon above after the [`PyObject_HEAD`](../c-api/structures.xhtml#c.PyObject_HEAD "PyObject_HEAD") macro. Be wary of adding one by accident: some compilers will complain.
Of course, objects generally store additional data besides the standard `PyObject_HEAD` boilerplate; for example, here is the definition for standard Python floats:
```
typedef struct {
PyObject_HEAD
double ob_fval;
} PyFloatObject;
```
The second bit is the definition of the type object.
```
static PyTypeObject CustomType = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "custom.Custom",
.tp_doc = "Custom objects",
.tp_basicsize = sizeof(CustomObject),
.tp_itemsize = 0,
.tp_flags = Py_TPFLAGS_DEFAULT,
.tp_new = PyType_GenericNew,
};
```
注解
We recommend using C99-style designated initializers as above, to avoid listing all the [`PyTypeObject`](../c-api/type.xhtml#c.PyTypeObject "PyTypeObject") fields that you don't care about and also to avoid caring about the fields' declaration order.
The actual definition of [`PyTypeObject`](../c-api/type.xhtml#c.PyTypeObject "PyTypeObject") in `object.h` has many more [fields](../c-api/typeobj.xhtml#type-structs) than the definition above. The remaining fields will be filled with zeros by the C compiler, and it's common practice to not specify them explicitly unless you need them.
We're going to pick it apart, one field at a time:
```
PyVarObject_HEAD_INIT(NULL, 0)
```
This line is mandatory boilerplate to initialize the `ob_base`field mentioned above.
```
.tp_name = "custom.Custom",
```
The name of our type. This will appear in the default textual representation of our objects and in some error messages, for example:
```
>>> "" + custom.Custom()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: can only concatenate str (not "custom.Custom") to str
```
Note that the name is a dotted name that includes both the module name and the name of the type within the module. The module in this case is `custom` and the type is `Custom`, so we set the type name to `custom.Custom`. Using the real dotted import path is important to make your type compatible with the [`pydoc`](../library/pydoc.xhtml#module-pydoc "pydoc: Documentation generator and online help system.") and [`pickle`](../library/pickle.xhtml#module-pickle "pickle: Convert Python objects to streams of bytes and back.") modules.
```
.tp_basicsize = sizeof(CustomObject),
.tp_itemsize = 0,
```
This is so that Python knows how much memory to allocate when creating new `Custom` instances. [`tp_itemsize`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_itemsize "PyTypeObject.tp_itemsize") is only used for variable-sized objects and should otherwise be zero.
注解
If you want your type to be subclassable from Python, and your type has the same [`tp_basicsize`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_basicsize "PyTypeObject.tp_basicsize") as its base type, you may have problems with multiple inheritance. A Python subclass of your type will have to list your type first in its [`__bases__`](../library/stdtypes.xhtml#class.__bases__ "class.__bases__"), or else it will not be able to call your type's [`__new__()`](../reference/datamodel.xhtml#object.__new__ "object.__new__") method without getting an error. You can avoid this problem by ensuring that your type has a larger value for [`tp_basicsize`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_basicsize "PyTypeObject.tp_basicsize") than its base type does. Most of the time, this will be true anyway, because either your base type will be [`object`](../library/functions.xhtml#object "object"), or else you will be adding data members to your base type, and therefore increasing its size.
We set the class flags to [`Py_TPFLAGS_DEFAULT`](../c-api/typeobj.xhtml#Py_TPFLAGS_DEFAULT "Py_TPFLAGS_DEFAULT").
```
.tp_flags = Py_TPFLAGS_DEFAULT,
```
All types should include this constant in their flags. It enables all of the members defined until at least Python 3.3. If you need further members, you will need to OR the corresponding flags.
We provide a doc string for the type in [`tp_doc`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_doc "PyTypeObject.tp_doc").
```
.tp_doc = "Custom objects",
```
To enable object creation, we have to provide a [`tp_new`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_new "PyTypeObject.tp_new")handler. This is the equivalent of the Python method [`__new__()`](../reference/datamodel.xhtml#object.__new__ "object.__new__"), but has to be specified explicitly. In this case, we can just use the default implementation provided by the API function [`PyType_GenericNew()`](../c-api/type.xhtml#c.PyType_GenericNew "PyType_GenericNew").
```
.tp_new = PyType_GenericNew,
```
Everything else in the file should be familiar, except for some code in `PyInit_custom()`:
```
if (PyType_Ready(&CustomType) < 0)
return;
```
This initializes the `Custom` type, filling in a number of members to the appropriate default values, including `ob_type` that we initially set to *NULL*.
```
PyModule_AddObject(m, "Custom", (PyObject *) &CustomType);
```
This adds the type to the module dictionary. This allows us to create `Custom` instances by calling the `Custom` class:
```
>>> import custom
>>> mycustom = custom.Custom()
```
That's it! All that remains is to build it; put the above code in a file called `custom.c` and:
```
from distutils.core import setup, Extension
setup(name="custom", version="1.0",
ext_modules=[Extension("custom", ["custom.c"])])
```
in a file called `setup.py`; then typing
```
$ python setup.py build
```
at a shell should produce a file `custom.so` in a subdirectory; move to that directory and fire up Python --- you should be able to `import custom` and play around with Custom objects.
That wasn't so hard, was it?
Of course, the current Custom type is pretty uninteresting. It has no data and doesn't do anything. It can't even be subclassed.
注解
While this documentation showcases the standard [`distutils`](../library/distutils.xhtml#module-distutils "distutils: Support for building and installing Python modules into an existing Python installation.") module for building C extensions, it is recommended in real-world use cases to use the newer and better-maintained `setuptools` library. Documentation on how to do this is out of scope for this document and can be found in the [Python Packaging User's Guide](https://packaging.python.org/tutorials/distributing-packages/) \[https://packaging.python.org/tutorials/distributing-packages/\].
## 2.2. Adding data and methods to the Basic example
Let's extend the basic example to add some data and methods. Let's also make the type usable as a base class. We'll create a new module, `custom2` that adds these capabilities:
```
#define PY_SSIZE_T_CLEAN
#include <Python.h>
#include "structmember.h"
typedef struct {
PyObject_HEAD
PyObject *first; /* first name */
PyObject *last; /* last name */
int number;
} CustomObject;
static void
Custom_dealloc(CustomObject *self)
{
Py_XDECREF(self->first);
Py_XDECREF(self->last);
Py_TYPE(self)->tp_free((PyObject *) self);
}
static PyObject *
Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
CustomObject *self;
self = (CustomObject *) type->tp_alloc(type, 0);
if (self != NULL) {
self->first = PyUnicode_FromString("");
if (self->first == NULL) {
Py_DECREF(self);
return NULL;
}
self->last = PyUnicode_FromString("");
if (self->last == NULL) {
Py_DECREF(self);
return NULL;
}
self->number = 0;
}
return (PyObject *) self;
}
static int
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
{
static char *kwlist[] = {"first", "last", "number", NULL};
PyObject *first = NULL, *last = NULL, *tmp;
if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OOi", kwlist,
&first, &last,
&self->number))
return -1;
if (first) {
tmp = self->first;
Py_INCREF(first);
self->first = first;
Py_XDECREF(tmp);
}
if (last) {
tmp = self->last;
Py_INCREF(last);
self->last = last;
Py_XDECREF(tmp);
}
return 0;
}
static PyMemberDef Custom_members[] = {
{"first", T_OBJECT_EX, offsetof(CustomObject, first), 0,
"first name"},
{"last", T_OBJECT_EX, offsetof(CustomObject, last), 0,
"last name"},
{"number", T_INT, offsetof(CustomObject, number), 0,
"custom number"},
{NULL} /* Sentinel */
};
static PyObject *
Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
{
if (self->first == NULL) {
PyErr_SetString(PyExc_AttributeError, "first");
return NULL;
}
if (self->last == NULL) {
PyErr_SetString(PyExc_AttributeError, "last");
return NULL;
}
return PyUnicode_FromFormat("%S %S", self->first, self->last);
}
static PyMethodDef Custom_methods[] = {
{"name", (PyCFunction) Custom_name, METH_NOARGS,
"Return the name, combining the first and last name"
},
{NULL} /* Sentinel */
};
static PyTypeObject CustomType = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "custom2.Custom",
.tp_doc = "Custom objects",
.tp_basicsize = sizeof(CustomObject),
.tp_itemsize = 0,
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
.tp_new = Custom_new,
.tp_init = (initproc) Custom_init,
.tp_dealloc = (destructor) Custom_dealloc,
.tp_members = Custom_members,
.tp_methods = Custom_methods,
};
static PyModuleDef custommodule = {
PyModuleDef_HEAD_INIT,
.m_name = "custom2",
.m_doc = "Example module that creates an extension type.",
.m_size = -1,
};
PyMODINIT_FUNC
PyInit_custom2(void)
{
PyObject *m;
if (PyType_Ready(&CustomType) < 0)
return NULL;
m = PyModule_Create(&custommodule);
if (m == NULL)
return NULL;
Py_INCREF(&CustomType);
PyModule_AddObject(m, "Custom", (PyObject *) &CustomType);
return m;
}
```
This version of the module has a number of changes.
We've added an extra include:
```
#include <structmember.h>
```
This include provides declarations that we use to handle attributes, as described a bit later.
The `Custom` type now has three data attributes in its C struct, *first*, *last*, and *number*. The *first* and *last* variables are Python strings containing first and last names. The *number* attribute is a C integer.
The object structure is updated accordingly:
```
typedef struct {
PyObject_HEAD
PyObject *first; /* first name */
PyObject *last; /* last name */
int number;
} CustomObject;
```
Because we now have data to manage, we have to be more careful about object allocation and deallocation. At a minimum, we need a deallocation method:
```
static void
Custom_dealloc(CustomObject *self)
{
Py_XDECREF(self->first);
Py_XDECREF(self->last);
Py_TYPE(self)->tp_free((PyObject *) self);
}
```
which is assigned to the [`tp_dealloc`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_dealloc "PyTypeObject.tp_dealloc") member:
```
.tp_dealloc = (destructor) Custom_dealloc,
```
This method first clears the reference counts of the two Python attributes. [`Py_XDECREF()`](../c-api/refcounting.xhtml#c.Py_XDECREF "Py_XDECREF") correctly handles the case where its argument is *NULL* (which might happen here if `tp_new` failed midway). It then calls the [`tp_free`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_free "PyTypeObject.tp_free") member of the object's type (computed by `Py_TYPE(self)`) to free the object's memory. Note that the object's type might not be `CustomType`, because the object may be an instance of a subclass.
注解
The explicit cast to `destructor` above is needed because we defined `Custom_dealloc` to take a `CustomObject *` argument, but the `tp_dealloc`function pointer expects to receive a `PyObject *` argument. Otherwise, the compiler will emit a warning. This is object-oriented polymorphism, in C!
We want to make sure that the first and last names are initialized to empty strings, so we provide a `tp_new` implementation:
```
static PyObject *
Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
CustomObject *self;
self = (CustomObject *) type->tp_alloc(type, 0);
if (self != NULL) {
self->first = PyUnicode_FromString("");
if (self->first == NULL) {
Py_DECREF(self);
return NULL;
}
self->last = PyUnicode_FromString("");
if (self->last == NULL) {
Py_DECREF(self);
return NULL;
}
self->number = 0;
}
return (PyObject *) self;
}
```
and install it in the [`tp_new`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_new "PyTypeObject.tp_new") member:
```
.tp_new = Custom_new,
```
The `tp_new` handler is responsible for creating (as opposed to initializing) objects of the type. It is exposed in Python as the [`__new__()`](../reference/datamodel.xhtml#object.__new__ "object.__new__") method. It is not required to define a `tp_new` member, and indeed many extension types will simply reuse [`PyType_GenericNew()`](../c-api/type.xhtml#c.PyType_GenericNew "PyType_GenericNew") as done in the first version of the `Custom` type above. In this case, we use the `tp_new`handler to initialize the `first` and `last` attributes to non-*NULL*default values.
`tp_new` is passed the type being instantiated (not necessarily `CustomType`, if a subclass is instantiated) and any arguments passed when the type was called, and is expected to return the instance created. `tp_new` handlers always accept positional and keyword arguments, but they often ignore the arguments, leaving the argument handling to initializer (a.k.a. `tp_init`in C or `__init__` in Python) methods.
注解
`tp_new` shouldn't call `tp_init` explicitly, as the interpreter will do it itself.
The `tp_new` implementation calls the [`tp_alloc`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_alloc "PyTypeObject.tp_alloc")slot to allocate memory:
```
self = (CustomObject *) type->tp_alloc(type, 0);
```
Since memory allocation may fail, we must check the [`tp_alloc`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_alloc "PyTypeObject.tp_alloc")result against *NULL* before proceeding.
注解
We didn't fill the [`tp_alloc`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_alloc "PyTypeObject.tp_alloc") slot ourselves. Rather [`PyType_Ready()`](../c-api/type.xhtml#c.PyType_Ready "PyType_Ready") fills it for us by inheriting it from our base class, which is [`object`](../library/functions.xhtml#object "object") by default. Most types use the default allocation strategy.
注解
If you are creating a co-operative [`tp_new`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_new "PyTypeObject.tp_new") (one that calls a base type's [`tp_new`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_new "PyTypeObject.tp_new") or [`__new__()`](../reference/datamodel.xhtml#object.__new__ "object.__new__")), you must *not* try to determine what method to call using method resolution order at runtime. Always statically determine what type you are going to call, and call its [`tp_new`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_new "PyTypeObject.tp_new") directly, or via `type->tp_base->tp_new`. If you do not do this, Python subclasses of your type that also inherit from other Python-defined classes may not work correctly. (Specifically, you may not be able to create instances of such subclasses without getting a [`TypeError`](../library/exceptions.xhtml#TypeError "TypeError").)
We also define an initialization function which accepts arguments to provide initial values for our instance:
```
static int
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
{
static char *kwlist[] = {"first", "last", "number", NULL};
PyObject *first = NULL, *last = NULL, *tmp;
if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OOi", kwlist,
&first, &last,
&self->number))
return -1;
if (first) {
tmp = self->first;
Py_INCREF(first);
self->first = first;
Py_XDECREF(tmp);
}
if (last) {
tmp = self->last;
Py_INCREF(last);
self->last = last;
Py_XDECREF(tmp);
}
return 0;
}
```
by filling the [`tp_init`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_init "PyTypeObject.tp_init") slot.
```
.tp_init = (initproc) Custom_init,
```
The [`tp_init`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_init "PyTypeObject.tp_init") slot is exposed in Python as the [`__init__()`](../reference/datamodel.xhtml#object.__init__ "object.__init__") method. It is used to initialize an object after it's created. Initializers always accept positional and keyword arguments, and they should return either `0` on success or `-1` on error.
Unlike the `tp_new` handler, there is no guarantee that `tp_init`is called at all (for example, the [`pickle`](../library/pickle.xhtml#module-pickle "pickle: Convert Python objects to streams of bytes and back.") module by default doesn't call [`__init__()`](../reference/datamodel.xhtml#object.__init__ "object.__init__") on unpickled instances). It can also be called multiple times. Anyone can call the [`__init__()`](../reference/datamodel.xhtml#object.__init__ "object.__init__") method on our objects. For this reason, we have to be extra careful when assigning the new attribute values. We might be tempted, for example to assign the `first` member like this:
```
if (first) {
Py_XDECREF(self->first);
Py_INCREF(first);
self->first = first;
}
```
But this would be risky. Our type doesn't restrict the type of the `first` member, so it could be any kind of object. It could have a destructor that causes code to be executed that tries to access the `first` member; or that destructor could release the [Global interpreter Lock](../glossary.xhtml#term-global-interpreter-lock) and let arbitrary code run in other threads that accesses and modifies our object.
To be paranoid and protect ourselves against this possibility, we almost always reassign members before decrementing their reference counts. When don't we have to do this?
- when we absolutely know that the reference count is greater than 1;
- when we know that deallocation of the object [1](#id5) will neither release the [GIL](../glossary.xhtml#term-gil) nor cause any calls back into our type's code;
- when decrementing a reference count in a [`tp_dealloc`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_dealloc "PyTypeObject.tp_dealloc")handler on a type which doesn't support cyclic garbage collection [2](#id6).
We want to expose our instance variables as attributes. There are a number of ways to do that. The simplest way is to define member definitions:
```
static PyMemberDef Custom_members[] = {
{"first", T_OBJECT_EX, offsetof(CustomObject, first), 0,
"first name"},
{"last", T_OBJECT_EX, offsetof(CustomObject, last), 0,
"last name"},
{"number", T_INT, offsetof(CustomObject, number), 0,
"custom number"},
{NULL} /* Sentinel */
};
```
and put the definitions in the [`tp_members`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_members "PyTypeObject.tp_members") slot:
```
.tp_members = Custom_members,
```
Each member definition has a member name, type, offset, access flags and documentation string. See the [Generic Attribute Management](newtypes.xhtml#generic-attribute-management) section below for details.
A disadvantage of this approach is that it doesn't provide a way to restrict the types of objects that can be assigned to the Python attributes. We expect the first and last names to be strings, but any Python objects can be assigned. Further, the attributes can be deleted, setting the C pointers to *NULL*. Even though we can make sure the members are initialized to non-*NULL* values, the members can be set to *NULL* if the attributes are deleted.
We define a single method, `Custom.name()`, that outputs the objects name as the concatenation of the first and last names.
```
static PyObject *
Custom_name(CustomObject *self)
{
if (self->first == NULL) {
PyErr_SetString(PyExc_AttributeError, "first");
return NULL;
}
if (self->last == NULL) {
PyErr_SetString(PyExc_AttributeError, "last");
return NULL;
}
return PyUnicode_FromFormat("%S %S", self->first, self->last);
}
```
The method is implemented as a C function that takes a `Custom` (or `Custom` subclass) instance as the first argument. Methods always take an instance as the first argument. Methods often take positional and keyword arguments as well, but in this case we don't take any and don't need to accept a positional argument tuple or keyword argument dictionary. This method is equivalent to the Python method:
```
def name(self):
return "%s %s" % (self.first, self.last)
```
Note that we have to check for the possibility that our `first` and `last` members are *NULL*. This is because they can be deleted, in which case they are set to *NULL*. It would be better to prevent deletion of these attributes and to restrict the attribute values to be strings. We'll see how to do that in the next section.
Now that we've defined the method, we need to create an array of method definitions:
```
static PyMethodDef Custom_methods[] = {
{"name", (PyCFunction) Custom_name, METH_NOARGS,
"Return the name, combining the first and last name"
},
{NULL} /* Sentinel */
};
```
(note that we used the [`METH_NOARGS`](../c-api/structures.xhtml#METH_NOARGS "METH_NOARGS") flag to indicate that the method is expecting no arguments other than *self*)
and assign it to the [`tp_methods`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_methods "PyTypeObject.tp_methods") slot:
```
.tp_methods = Custom_methods,
```
Finally, we'll make our type usable as a base class for subclassing. We've written our methods carefully so far so that they don't make any assumptions about the type of the object being created or used, so all we need to do is to add the [`Py_TPFLAGS_BASETYPE`](../c-api/typeobj.xhtml#Py_TPFLAGS_BASETYPE "Py_TPFLAGS_BASETYPE") to our class flag definition:
```
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
```
We rename `PyInit_custom()` to `PyInit_custom2()`, update the module name in the [`PyModuleDef`](../c-api/module.xhtml#c.PyModuleDef "PyModuleDef") struct, and update the full class name in the [`PyTypeObject`](../c-api/type.xhtml#c.PyTypeObject "PyTypeObject") struct.
Finally, we update our `setup.py` file to build the new module:
```
from distutils.core import setup, Extension
setup(name="custom", version="1.0",
ext_modules=[
Extension("custom", ["custom.c"]),
Extension("custom2", ["custom2.c"]),
])
```
## 2.3. Providing finer control over data attributes
In this section, we'll provide finer control over how the `first` and `last` attributes are set in the `Custom` example. In the previous version of our module, the instance variables `first` and `last`could be set to non-string values or even deleted. We want to make sure that these attributes always contain strings.
```
#define PY_SSIZE_T_CLEAN
#include <Python.h>
#include "structmember.h"
typedef struct {
PyObject_HEAD
PyObject *first; /* first name */
PyObject *last; /* last name */
int number;
} CustomObject;
static void
Custom_dealloc(CustomObject *self)
{
Py_XDECREF(self->first);
Py_XDECREF(self->last);
Py_TYPE(self)->tp_free((PyObject *) self);
}
static PyObject *
Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
CustomObject *self;
self = (CustomObject *) type->tp_alloc(type, 0);
if (self != NULL) {
self->first = PyUnicode_FromString("");
if (self->first == NULL) {
Py_DECREF(self);
return NULL;
}
self->last = PyUnicode_FromString("");
if (self->last == NULL) {
Py_DECREF(self);
return NULL;
}
self->number = 0;
}
return (PyObject *) self;
}
static int
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
{
static char *kwlist[] = {"first", "last", "number", NULL};
PyObject *first = NULL, *last = NULL, *tmp;
if (!PyArg_ParseTupleAndKeywords(args, kwds, "|UUi", kwlist,
&first, &last,
&self->number))
return -1;
if (first) {
tmp = self->first;
Py_INCREF(first);
self->first = first;
Py_DECREF(tmp);
}
if (last) {
tmp = self->last;
Py_INCREF(last);
self->last = last;
Py_DECREF(tmp);
}
return 0;
}
static PyMemberDef Custom_members[] = {
{"number", T_INT, offsetof(CustomObject, number), 0,
"custom number"},
{NULL} /* Sentinel */
};
static PyObject *
Custom_getfirst(CustomObject *self, void *closure)
{
Py_INCREF(self->first);
return self->first;
}
static int
Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
{
PyObject *tmp;
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
return -1;
}
if (!PyUnicode_Check(value)) {
PyErr_SetString(PyExc_TypeError,
"The first attribute value must be a string");
return -1;
}
tmp = self->first;
Py_INCREF(value);
self->first = value;
Py_DECREF(tmp);
return 0;
}
static PyObject *
Custom_getlast(CustomObject *self, void *closure)
{
Py_INCREF(self->last);
return self->last;
}
static int
Custom_setlast(CustomObject *self, PyObject *value, void *closure)
{
PyObject *tmp;
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the last attribute");
return -1;
}
if (!PyUnicode_Check(value)) {
PyErr_SetString(PyExc_TypeError,
"The last attribute value must be a string");
return -1;
}
tmp = self->last;
Py_INCREF(value);
self->last = value;
Py_DECREF(tmp);
return 0;
}
static PyGetSetDef Custom_getsetters[] = {
{"first", (getter) Custom_getfirst, (setter) Custom_setfirst,
"first name", NULL},
{"last", (getter) Custom_getlast, (setter) Custom_setlast,
"last name", NULL},
{NULL} /* Sentinel */
};
static PyObject *
Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
{
return PyUnicode_FromFormat("%S %S", self->first, self->last);
}
static PyMethodDef Custom_methods[] = {
{"name", (PyCFunction) Custom_name, METH_NOARGS,
"Return the name, combining the first and last name"
},
{NULL} /* Sentinel */
};
static PyTypeObject CustomType = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "custom3.Custom",
.tp_doc = "Custom objects",
.tp_basicsize = sizeof(CustomObject),
.tp_itemsize = 0,
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
.tp_new = Custom_new,
.tp_init = (initproc) Custom_init,
.tp_dealloc = (destructor) Custom_dealloc,
.tp_members = Custom_members,
.tp_methods = Custom_methods,
.tp_getset = Custom_getsetters,
};
static PyModuleDef custommodule = {
PyModuleDef_HEAD_INIT,
.m_name = "custom3",
.m_doc = "Example module that creates an extension type.",
.m_size = -1,
};
PyMODINIT_FUNC
PyInit_custom3(void)
{
PyObject *m;
if (PyType_Ready(&CustomType) < 0)
return NULL;
m = PyModule_Create(&custommodule);
if (m == NULL)
return NULL;
Py_INCREF(&CustomType);
PyModule_AddObject(m, "Custom", (PyObject *) &CustomType);
return m;
}
```
To provide greater control, over the `first` and `last` attributes, we'll use custom getter and setter functions. Here are the functions for getting and setting the `first` attribute:
```
static PyObject *
Custom_getfirst(CustomObject *self, void *closure)
{
Py_INCREF(self->first);
return self->first;
}
static int
Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
{
PyObject *tmp;
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
return -1;
}
if (!PyUnicode_Check(value)) {
PyErr_SetString(PyExc_TypeError,
"The first attribute value must be a string");
return -1;
}
tmp = self->first;
Py_INCREF(value);
self->first = value;
Py_DECREF(tmp);
return 0;
}
```
The getter function is passed a `Custom` object and a "closure", which is a void pointer. In this case, the closure is ignored. (The closure supports an advanced usage in which definition data is passed to the getter and setter. This could, for example, be used to allow a single set of getter and setter functions that decide the attribute to get or set based on data in the closure.)
The setter function is passed the `Custom` object, the new value, and the closure. The new value may be *NULL*, in which case the attribute is being deleted. In our setter, we raise an error if the attribute is deleted or if its new value is not a string.
We create an array of [`PyGetSetDef`](../c-api/structures.xhtml#c.PyGetSetDef "PyGetSetDef") structures:
```
static PyGetSetDef Custom_getsetters[] = {
{"first", (getter) Custom_getfirst, (setter) Custom_setfirst,
"first name", NULL},
{"last", (getter) Custom_getlast, (setter) Custom_setlast,
"last name", NULL},
{NULL} /* Sentinel */
};
```
and register it in the [`tp_getset`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_getset "PyTypeObject.tp_getset") slot:
```
.tp_getset = Custom_getsetters,
```
The last item in a [`PyGetSetDef`](../c-api/structures.xhtml#c.PyGetSetDef "PyGetSetDef") structure is the "closure" mentioned above. In this case, we aren't using a closure, so we just pass *NULL*.
We also remove the member definitions for these attributes:
```
static PyMemberDef Custom_members[] = {
{"number", T_INT, offsetof(CustomObject, number), 0,
"custom number"},
{NULL} /* Sentinel */
};
```
We also need to update the [`tp_init`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_init "PyTypeObject.tp_init") handler to only allow strings [3](#id7) to be passed:
```
static int
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
{
static char *kwlist[] = {"first", "last", "number", NULL};
PyObject *first = NULL, *last = NULL, *tmp;
if (!PyArg_ParseTupleAndKeywords(args, kwds, "|UUi", kwlist,
&first, &last,
&self->number))
return -1;
if (first) {
tmp = self->first;
Py_INCREF(first);
self->first = first;
Py_DECREF(tmp);
}
if (last) {
tmp = self->last;
Py_INCREF(last);
self->last = last;
Py_DECREF(tmp);
}
return 0;
}
```
With these changes, we can assure that the `first` and `last` members are never *NULL* so we can remove checks for *NULL* values in almost all cases. This means that most of the [`Py_XDECREF()`](../c-api/refcounting.xhtml#c.Py_XDECREF "Py_XDECREF") calls can be converted to [`Py_DECREF()`](../c-api/refcounting.xhtml#c.Py_DECREF "Py_DECREF") calls. The only place we can't change these calls is in the `tp_dealloc` implementation, where there is the possibility that the initialization of these members failed in `tp_new`.
We also rename the module initialization function and module name in the initialization function, as we did before, and we add an extra definition to the `setup.py` file.
## 2.4. Supporting cyclic garbage collection
Python has a [cyclic garbage collector (GC)](../glossary.xhtml#term-garbage-collection) that can identify unneeded objects even when their reference counts are not zero. This can happen when objects are involved in cycles. For example, consider:
```
>>> l = []
>>> l.append(l)
>>> del l
```
In this example, we create a list that contains itself. When we delete it, it still has a reference from itself. Its reference count doesn't drop to zero. Fortunately, Python's cyclic garbage collector will eventually figure out that the list is garbage and free it.
In the second version of the `Custom` example, we allowed any kind of object to be stored in the `first` or `last` attributes [4](#id8). Besides, in the second and third versions, we allowed subclassing `Custom`, and subclasses may add arbitrary attributes. For any of those two reasons, `Custom` objects can participate in cycles:
```
>>> import custom3
>>> class Derived(custom3.Custom): pass
...
>>> n = Derived()
>>> n.some_attribute = n
```
To allow a `Custom` instance participating in a reference cycle to be properly detected and collected by the cyclic GC, our `Custom` type needs to fill two additional slots and to enable a flag that enables these slots:
```
#define PY_SSIZE_T_CLEAN
#include <Python.h>
#include "structmember.h"
typedef struct {
PyObject_HEAD
PyObject *first; /* first name */
PyObject *last; /* last name */
int number;
} CustomObject;
static int
Custom_traverse(CustomObject *self, visitproc visit, void *arg)
{
Py_VISIT(self->first);
Py_VISIT(self->last);
return 0;
}
static int
Custom_clear(CustomObject *self)
{
Py_CLEAR(self->first);
Py_CLEAR(self->last);
return 0;
}
static void
Custom_dealloc(CustomObject *self)
{
PyObject_GC_UnTrack(self);
Custom_clear(self);
Py_TYPE(self)->tp_free((PyObject *) self);
}
static PyObject *
Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
CustomObject *self;
self = (CustomObject *) type->tp_alloc(type, 0);
if (self != NULL) {
self->first = PyUnicode_FromString("");
if (self->first == NULL) {
Py_DECREF(self);
return NULL;
}
self->last = PyUnicode_FromString("");
if (self->last == NULL) {
Py_DECREF(self);
return NULL;
}
self->number = 0;
}
return (PyObject *) self;
}
static int
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
{
static char *kwlist[] = {"first", "last", "number", NULL};
PyObject *first = NULL, *last = NULL, *tmp;
if (!PyArg_ParseTupleAndKeywords(args, kwds, "|UUi", kwlist,
&first, &last,
&self->number))
return -1;
if (first) {
tmp = self->first;
Py_INCREF(first);
self->first = first;
Py_DECREF(tmp);
}
if (last) {
tmp = self->last;
Py_INCREF(last);
self->last = last;
Py_DECREF(tmp);
}
return 0;
}
static PyMemberDef Custom_members[] = {
{"number", T_INT, offsetof(CustomObject, number), 0,
"custom number"},
{NULL} /* Sentinel */
};
static PyObject *
Custom_getfirst(CustomObject *self, void *closure)
{
Py_INCREF(self->first);
return self->first;
}
static int
Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
{
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
return -1;
}
if (!PyUnicode_Check(value)) {
PyErr_SetString(PyExc_TypeError,
"The first attribute value must be a string");
return -1;
}
Py_INCREF(value);
Py_CLEAR(self->first);
self->first = value;
return 0;
}
static PyObject *
Custom_getlast(CustomObject *self, void *closure)
{
Py_INCREF(self->last);
return self->last;
}
static int
Custom_setlast(CustomObject *self, PyObject *value, void *closure)
{
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the last attribute");
return -1;
}
if (!PyUnicode_Check(value)) {
PyErr_SetString(PyExc_TypeError,
"The last attribute value must be a string");
return -1;
}
Py_INCREF(value);
Py_CLEAR(self->last);
self->last = value;
return 0;
}
static PyGetSetDef Custom_getsetters[] = {
{"first", (getter) Custom_getfirst, (setter) Custom_setfirst,
"first name", NULL},
{"last", (getter) Custom_getlast, (setter) Custom_setlast,
"last name", NULL},
{NULL} /* Sentinel */
};
static PyObject *
Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
{
return PyUnicode_FromFormat("%S %S", self->first, self->last);
}
static PyMethodDef Custom_methods[] = {
{"name", (PyCFunction) Custom_name, METH_NOARGS,
"Return the name, combining the first and last name"
},
{NULL} /* Sentinel */
};
static PyTypeObject CustomType = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "custom4.Custom",
.tp_doc = "Custom objects",
.tp_basicsize = sizeof(CustomObject),
.tp_itemsize = 0,
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,
.tp_new = Custom_new,
.tp_init = (initproc) Custom_init,
.tp_dealloc = (destructor) Custom_dealloc,
.tp_traverse = (traverseproc) Custom_traverse,
.tp_clear = (inquiry) Custom_clear,
.tp_members = Custom_members,
.tp_methods = Custom_methods,
.tp_getset = Custom_getsetters,
};
static PyModuleDef custommodule = {
PyModuleDef_HEAD_INIT,
.m_name = "custom4",
.m_doc = "Example module that creates an extension type.",
.m_size = -1,
};
PyMODINIT_FUNC
PyInit_custom4(void)
{
PyObject *m;
if (PyType_Ready(&CustomType) < 0)
return NULL;
m = PyModule_Create(&custommodule);
if (m == NULL)
return NULL;
Py_INCREF(&CustomType);
PyModule_AddObject(m, "Custom", (PyObject *) &CustomType);
return m;
}
```
First, the traversal method lets the cyclic GC know about subobjects that could participate in cycles:
```
static int
Custom_traverse(CustomObject *self, visitproc visit, void *arg)
{
int vret;
if (self->first) {
vret = visit(self->first, arg);
if (vret != 0)
return vret;
}
if (self->last) {
vret = visit(self->last, arg);
if (vret != 0)
return vret;
}
return 0;
}
```
For each subobject that can participate in cycles, we need to call the `visit()` function, which is passed to the traversal method. The `visit()` function takes as arguments the subobject and the extra argument *arg* passed to the traversal method. It returns an integer value that must be returned if it is non-zero.
Python provides a [`Py_VISIT()`](../c-api/gcsupport.xhtml#c.Py_VISIT "Py_VISIT") macro that automates calling visit functions. With [`Py_VISIT()`](../c-api/gcsupport.xhtml#c.Py_VISIT "Py_VISIT"), we can minimize the amount of boilerplate in `Custom_traverse`:
```
static int
Custom_traverse(CustomObject *self, visitproc visit, void *arg)
{
Py_VISIT(self->first);
Py_VISIT(self->last);
return 0;
}
```
注解
The [`tp_traverse`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_traverse "PyTypeObject.tp_traverse") implementation must name its arguments exactly *visit* and *arg* in order to use [`Py_VISIT()`](../c-api/gcsupport.xhtml#c.Py_VISIT "Py_VISIT").
Second, we need to provide a method for clearing any subobjects that can participate in cycles:
```
static int
Custom_clear(CustomObject *self)
{
Py_CLEAR(self->first);
Py_CLEAR(self->last);
return 0;
}
```
Notice the use of the [`Py_CLEAR()`](../c-api/refcounting.xhtml#c.Py_CLEAR "Py_CLEAR") macro. It is the recommended and safe way to clear data attributes of arbitrary types while decrementing their reference counts. If you were to call [`Py_XDECREF()`](../c-api/refcounting.xhtml#c.Py_XDECREF "Py_XDECREF") instead on the attribute before setting it to *NULL*, there is a possibility that the attribute's destructor would call back into code that reads the attribute again (*especially* if there is a reference cycle).
注解
You could emulate [`Py_CLEAR()`](../c-api/refcounting.xhtml#c.Py_CLEAR "Py_CLEAR") by writing:
```
PyObject *tmp;
tmp = self->first;
self->first = NULL;
Py_XDECREF(tmp);
```
Nevertheless, it is much easier and less error-prone to always use [`Py_CLEAR()`](../c-api/refcounting.xhtml#c.Py_CLEAR "Py_CLEAR") when deleting an attribute. Don't try to micro-optimize at the expense of robustness!
The deallocator `Custom_dealloc` may call arbitrary code when clearing attributes. It means the circular GC can be triggered inside the function. Since the GC assumes reference count is not zero, we need to untrack the object from the GC by calling [`PyObject_GC_UnTrack()`](../c-api/gcsupport.xhtml#c.PyObject_GC_UnTrack "PyObject_GC_UnTrack") before clearing members. Here is our reimplemented deallocator using [`PyObject_GC_UnTrack()`](../c-api/gcsupport.xhtml#c.PyObject_GC_UnTrack "PyObject_GC_UnTrack")and `Custom_clear`:
```
static void
Custom_dealloc(CustomObject *self)
{
PyObject_GC_UnTrack(self);
Custom_clear(self);
Py_TYPE(self)->tp_free((PyObject *) self);
}
```
Finally, we add the [`Py_TPFLAGS_HAVE_GC`](../c-api/typeobj.xhtml#Py_TPFLAGS_HAVE_GC "Py_TPFLAGS_HAVE_GC") flag to the class flags:
```
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,
```
That's pretty much it. If we had written custom [`tp_alloc`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_alloc "PyTypeObject.tp_alloc") or [`tp_free`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_free "PyTypeObject.tp_free") handlers, we'd need to modify them for cyclic garbage collection. Most extensions will use the versions automatically provided.
## 2.5. Subclassing other types
It is possible to create new extension types that are derived from existing types. It is easiest to inherit from the built in types, since an extension can easily use the [`PyTypeObject`](../c-api/type.xhtml#c.PyTypeObject "PyTypeObject") it needs. It can be difficult to share these [`PyTypeObject`](../c-api/type.xhtml#c.PyTypeObject "PyTypeObject") structures between extension modules.
In this example we will create a `SubList` type that inherits from the built-in [`list`](../library/stdtypes.xhtml#list "list") type. The new type will be completely compatible with regular lists, but will have an additional `increment()` method that increases an internal counter:
```
>>> import sublist
>>> s = sublist.SubList(range(3))
>>> s.extend(s)
>>> print(len(s))
6
>>> print(s.increment())
1
>>> print(s.increment())
2
```
```
#define PY_SSIZE_T_CLEAN
#include <Python.h>
typedef struct {
PyListObject list;
int state;
} SubListObject;
static PyObject *
SubList_increment(SubListObject *self, PyObject *unused)
{
self->state++;
return PyLong_FromLong(self->state);
}
static PyMethodDef SubList_methods[] = {
{"increment", (PyCFunction) SubList_increment, METH_NOARGS,
PyDoc_STR("increment state counter")},
{NULL},
};
static int
SubList_init(SubListObject *self, PyObject *args, PyObject *kwds)
{
if (PyList_Type.tp_init((PyObject *) self, args, kwds) < 0)
return -1;
self->state = 0;
return 0;
}
static PyTypeObject SubListType = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "sublist.SubList",
.tp_doc = "SubList objects",
.tp_basicsize = sizeof(SubListObject),
.tp_itemsize = 0,
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
.tp_init = (initproc) SubList_init,
.tp_methods = SubList_methods,
};
static PyModuleDef sublistmodule = {
PyModuleDef_HEAD_INIT,
.m_name = "sublist",
.m_doc = "Example module that creates an extension type.",
.m_size = -1,
};
PyMODINIT_FUNC
PyInit_sublist(void)
{
PyObject *m;
SubListType.tp_base = &PyList_Type;
if (PyType_Ready(&SubListType) < 0)
return NULL;
m = PyModule_Create(&sublistmodule);
if (m == NULL)
return NULL;
Py_INCREF(&SubListType);
PyModule_AddObject(m, "SubList", (PyObject *) &SubListType);
return m;
}
```
As you can see, the source code closely resembles the `Custom` examples in previous sections. We will break down the main differences between them.
```
typedef struct {
PyListObject list;
int state;
} SubListObject;
```
The primary difference for derived type objects is that the base type's object structure must be the first value. The base type will already include the [`PyObject_HEAD()`](../c-api/structures.xhtml#c.PyObject_HEAD "PyObject_HEAD") at the beginning of its structure.
When a Python object is a `SubList` instance, its `PyObject *` pointer can be safely cast to both `PyListObject *` and `SubListObject *`:
```
static int
SubList_init(SubListObject *self, PyObject *args, PyObject *kwds)
{
if (PyList_Type.tp_init((PyObject *) self, args, kwds) < 0)
return -1;
self->state = 0;
return 0;
}
```
We see above how to call through to the `__init__` method of the base type.
This pattern is important when writing a type with custom [`tp_new`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_new "PyTypeObject.tp_new") and [`tp_dealloc`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_dealloc "PyTypeObject.tp_dealloc")members. The [`tp_new`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_new "PyTypeObject.tp_new") handler should not actually create the memory for the object with its [`tp_alloc`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_alloc "PyTypeObject.tp_alloc"), but let the base class handle it by calling its own [`tp_new`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_new "PyTypeObject.tp_new").
The [`PyTypeObject`](../c-api/type.xhtml#c.PyTypeObject "PyTypeObject") struct supports a [`tp_base`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_base "PyTypeObject.tp_base")specifying the type's concrete base class. Due to cross-platform compiler issues, you can't fill that field directly with a reference to [`PyList_Type`](../c-api/list.xhtml#c.PyList_Type "PyList_Type"); it should be done later in the module initialization function:
```
PyMODINIT_FUNC
PyInit_sublist(void)
{
PyObject* m;
SubListType.tp_base = &PyList_Type;
if (PyType_Ready(&SubListType) < 0)
return NULL;
m = PyModule_Create(&sublistmodule);
if (m == NULL)
return NULL;
Py_INCREF(&SubListType);
PyModule_AddObject(m, "SubList", (PyObject *) &SubListType);
return m;
}
```
Before calling [`PyType_Ready()`](../c-api/type.xhtml#c.PyType_Ready "PyType_Ready"), the type structure must have the [`tp_base`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_base "PyTypeObject.tp_base") slot filled in. When we are deriving an existing type, it is not necessary to fill out the [`tp_alloc`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_alloc "PyTypeObject.tp_alloc")slot with [`PyType_GenericNew()`](../c-api/type.xhtml#c.PyType_GenericNew "PyType_GenericNew") -- the allocation function from the base type will be inherited.
After that, calling [`PyType_Ready()`](../c-api/type.xhtml#c.PyType_Ready "PyType_Ready") and adding the type object to the module is the same as with the basic `Custom` examples.
脚注
[1](#id1)This is true when we know that the object is a basic type, like a string or a float.
[2](#id2)We relied on this in the [`tp_dealloc`](../c-api/typeobj.xhtml#c.PyTypeObject.tp_dealloc "PyTypeObject.tp_dealloc") handler in this example, because our type doesn't support garbage collection.
[3](#id3)We now know that the first and last members are strings, so perhaps we could be less careful about decrementing their reference counts, however, we accept instances of string subclasses. Even though deallocating normal strings won't call back into our objects, we can't guarantee that deallocating an instance of a string subclass won't call back into our objects.
[4](#id4)Also, even with our attributes restricted to strings instances, the user could pass arbitrary [`str`](../library/stdtypes.xhtml#str "str") subclasses and therefore still create reference cycles.
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- Python文档内容
- Python 有什么新变化？
- Python 3.7 有什么新变化
- 摘要 - 发布重点
- 新的特性
- 其他语言特性修改
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- Python 3.7.1 中的重要变化
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- Python 3.6.2 中的重要变化
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- PEP 405: Virtual Environments
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- PEP 3118: New memoryview implementation and buffer protocol documentation
- PEP 393: Flexible String Representation
- PEP 397: Python Launcher for Windows
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- Python 2.6 有什么新变化
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- PEP 366: Explicit Relative Imports From a Main Module
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- PEP 3105: print As a Function
- PEP 3110: Exception-Handling Changes
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- PEP 3118: Revised Buffer Protocol
- PEP 3119: Abstract Base Classes
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- PEP 3129: Class Decorators
- PEP 3141: A Type Hierarchy for Numbers
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- PEP 308: Conditional Expressions
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- PEP 314: Metadata for Python Software Packages v1.1
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- PEP 218: Built-In Set Objects
- PEP 237: Unifying Long Integers and Integers
- PEP 289: Generator Expressions
- PEP 292: Simpler String Substitutions
- PEP 318: Decorators for Functions and Methods
- PEP 322: Reverse Iteration
- PEP 324: New subprocess Module
- PEP 327: Decimal Data Type
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- 其他语言特性修改
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- Porting to Python 2.4
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- What's New in Python 2.3
- PEP 218: A Standard Set Datatype
- PEP 255: Simple Generators
- PEP 263: Source Code Encodings
- PEP 273: Importing Modules from ZIP Archives
- PEP 277: Unicode file name support for Windows NT
- PEP 278: Universal Newline Support
- PEP 279: enumerate()
- PEP 282: The logging Package
- PEP 285: A Boolean Type
- PEP 293: Codec Error Handling Callbacks
- PEP 301: Package Index and Metadata for Distutils
- PEP 302: New Import Hooks
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- Extended Slices
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- PEP 255: Simple Generators
- PEP 237: Unifying Long Integers and Integers
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- PEP 227: Nested Scopes
- New and Improved Modules
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- Acknowledgements
- What's New in Python 2.1
- 概述
- PEP 227: Nested Scopes
- PEP 236: future Directives
- PEP 207: Rich Comparisons
- PEP 230: Warning Framework
- PEP 229: New Build System
- PEP 205: Weak References
- PEP 232: Function Attributes
- PEP 235: Importing Modules on Case-Insensitive Platforms
- PEP 217: Interactive Display Hook
- PEP 208: New Coercion Model
- PEP 241: Metadata in Python Packages
- New and Improved Modules
- Other Changes and Fixes
- Acknowledgements
- What's New in Python 2.0
- 概述
- What About Python 1.6?
- New Development Process
- Unicode
- 列表推导式
- Augmented Assignment
- 字符串的方法
- Garbage Collection of Cycles
- Other Core Changes
- Porting to 2.0
- Extending/Embedding Changes
- Distutils: Making Modules Easy to Install
- XML Modules
- Module changes
- New modules
- IDLE Improvements
- Deleted and Deprecated Modules
- Acknowledgements
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- Python 下一版
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- Python 3.6.5 release candidate 1
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- Python 3.6.4 release candidate 1
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- Python 3.6.3 release candidate 1
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- Python 3.6.2 release candidate 2
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- Python 3.6.0 release candidate 1
- Python 3.6.0 beta 4
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- Python 3.5.0 beta 1
- Python 3.5.0 alpha 4
- Python 3.5.0 alpha 3
- Python 3.5.0 alpha 2
- Python 3.5.0 alpha 1
- Python 教程
- 课前甜点
- 使用 Python 解释器
- 调用解释器
- 解释器的运行环境
- Python 的非正式介绍
- Python 作为计算器使用
- 走向编程的第一步
- 其他流程控制工具
- if 语句
- for 语句
- range() 函数
- break 和 continue 语句，以及循环中的 else 子句
- pass 语句
- 定义函数
- 函数定义的更多形式
- 小插曲：编码风格
- 数据结构
- 列表的更多特性
- del 语句
- 元组和序列
- 集合
- 字典
- 循环的技巧
- 深入条件控制
- 序列和其它类型的比较
- 模块
- 有关模块的更多信息
- 标准模块
- dir() 函数
- 包
- 输入输出
- 更漂亮的输出格式
- 读写文件
- 错误和异常
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- 异常
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- 抛出异常
- 用户自定义异常
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- 预定义的清理操作
- 类
- 名称和对象
- Python 作用域和命名空间
- 初探类
- 补充说明
- 继承
- 私有变量
- 杂项说明
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- 生成器
- 生成器表达式
- 标准库简介
- 操作系统接口
- 文件通配符
- 命令行参数
- 错误输出重定向和程序终止
- 字符串模式匹配
- 数学
- 互联网访问
- 日期和时间
- 数据压缩
- 性能测量
- 质量控制
- 自带电池
- 标准库简介 —— 第二部分
- 格式化输出
- 模板
- 使用二进制数据记录格式
- 多线程
- 日志
- 弱引用
- 用于操作列表的工具
- 十进制浮点运算
- 虚拟环境和包
- 概述
- 创建虚拟环境
- 使用pip管理包
- 接下来？
- 交互式编辑和编辑历史
- Tab 补全和编辑历史
- 默认交互式解释器的替代品
- 浮点算术：争议和限制
- 表示性错误
- 附录
- 交互模式
- 安装和使用 Python
- 命令行与环境
- 命令行
- 环境变量
- 在Unix平台中使用Python
- 获取最新版本的Python
- 构建Python
- 与Python相关的路径和文件
- 杂项
- 编辑器和集成开发环境
- 在Windows上使用 Python
- 完整安装程序
- Microsoft Store包
- nuget.org 安装包
- 可嵌入的包
- 替代捆绑包
- 配置Python
- 适用于Windows的Python启动器
- 查找模块
- 附加模块
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- 其他平台
- 在苹果系统上使用 Python
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- IDE
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- Mac 上的图形界面编程
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- 标注
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- 字面值
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- 标准类型层级结构
- 特殊方法名称
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- 异常
- 导入系统
- importlib
- 包
- 搜索
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- 函数定义
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- 最高层级组件
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- 文件输入
- 交互式输入
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- 序列类型 — list, tuple, range
- 文本序列类型 — str
- 二进制序列类型 — bytes, bytearray, memoryview
- 集合类型 — set, frozenset
- 映射类型 — dict
- 上下文管理器类型
- 其他内置类型
- 特殊属性
- 内置异常
- 基类
- 具体异常
- 警告
- 异常层次结构
- 文本处理服务
- string — 常见的字符串操作
- re — 正则表达式操作
- 模块 difflib 是一个计算差异的助手
- textwrap — Text wrapping and filling
- unicodedata — Unicode 数据库
- stringprep — Internet String Preparation
- readline — GNU readline interface
- rlcompleter — GNU readline的完成函数
- 二进制数据服务
- struct — Interpret bytes as packed binary data
- codecs — Codec registry and base classes
- 数据类型
- datetime — 基础日期/时间数据类型
- calendar — General calendar-related functions
- collections — 容器数据类型
- collections.abc — 容器的抽象基类
- heapq — 堆队列算法
- bisect — Array bisection algorithm
- array — Efficient arrays of numeric values
- weakref — 弱引用
- types — Dynamic type creation and names for built-in types
- copy — 浅层 (shallow) 和深层 (deep) 复制操作
- pprint — 数据美化输出
- reprlib — Alternate repr() implementation
- enum — Support for enumerations
- 数字和数学模块
- numbers — 数字的抽象基类
- math — 数学函数
- cmath — Mathematical functions for complex numbers
- decimal — 十进制定点和浮点运算
- fractions — 分数
- random — 生成伪随机数
- statistics — Mathematical statistics functions
- 函数式编程模块
- itertools — 为高效循环而创建迭代器的函数
- functools — 高阶函数和可调用对象上的操作
- operator — 标准运算符替代函数
- 文件和目录访问
- pathlib — 面向对象的文件系统路径
- os.path — 常见路径操作
- fileinput — Iterate over lines from multiple input streams
- stat — Interpreting stat() results
- filecmp — File and Directory Comparisons
- tempfile — Generate temporary files and directories
- glob — Unix style pathname pattern expansion
- fnmatch — Unix filename pattern matching
- linecache — Random access to text lines
- shutil — High-level file operations
- macpath — Mac OS 9 路径操作函数
- 数据持久化
- pickle —— Python 对象序列化
- copyreg — Register pickle support functions
- shelve — Python object persistence
- marshal — Internal Python object serialization
- dbm — Interfaces to Unix “databases”
- sqlite3 — SQLite 数据库 DB-API 2.0 接口模块
- 数据压缩和存档
- zlib — 与 gzip 兼容的压缩
- gzip — 对 gzip 格式的支持
- bz2 — 对 bzip2 压缩算法的支持
- lzma — 用 LZMA 算法压缩
- zipfile — 在 ZIP 归档中工作
- tarfile — Read and write tar archive files
- 文件格式
- csv — CSV 文件读写
- configparser — Configuration file parser
- netrc — netrc file processing
- xdrlib — Encode and decode XDR data
- plistlib — Generate and parse Mac OS X .plist files
- 加密服务
- hashlib — 安全哈希与消息摘要
- hmac — 基于密钥的消息验证
- secrets — Generate secure random numbers for managing secrets
- 通用操作系统服务
- os — 操作系统接口模块
- io — 处理流的核心工具
- time — 时间的访问和转换
- argparse — 命令行选项、参数和子命令解析器
- getopt — C-style parser for command line options
- 模块 logging — Python 的日志记录工具
- logging.config — 日志记录配置
- logging.handlers — Logging handlers
- getpass — 便携式密码输入工具
- curses — 终端字符单元显示的处理
- curses.textpad — Text input widget for curses programs
- curses.ascii — Utilities for ASCII characters
- curses.panel — A panel stack extension for curses
- platform — Access to underlying platform's identifying data
- errno — Standard errno system symbols
- ctypes — Python 的外部函数库
- 并发执行
- threading — 基于线程的并行
- multiprocessing — 基于进程的并行
- concurrent 包
- concurrent.futures — 启动并行任务
- subprocess — 子进程管理
- sched — 事件调度器
- queue — 一个同步的队列类
- _thread — 底层多线程 API
- _dummy_thread — _thread 的替代模块
- dummy_threading — 可直接替代 threading 模块。
- contextvars — Context Variables
- Context Variables
- Manual Context Management
- asyncio support
- 网络和进程间通信
- asyncio — 异步 I/O
- socket — 底层网络接口
- ssl — TLS/SSL wrapper for socket objects
- select — Waiting for I/O completion
- selectors — 高级 I/O 复用库
- asyncore — 异步socket处理器
- asynchat — 异步 socket 指令/响应 处理器
- signal — Set handlers for asynchronous events
- mmap — Memory-mapped file support
- 互联网数据处理
- email — 电子邮件与 MIME 处理包
- json — JSON 编码和解码器
- mailcap — Mailcap file handling
- mailbox — Manipulate mailboxes in various formats
- mimetypes — Map filenames to MIME types
- base64 — Base16, Base32, Base64, Base85 数据编码
- binhex — 对binhex4文件进行编码和解码
- binascii — 二进制和 ASCII 码互转
- quopri — Encode and decode MIME quoted-printable data
- uu — Encode and decode uuencode files
- 结构化标记处理工具
- html — 超文本标记语言支持
- html.parser — 简单的 HTML 和 XHTML 解析器
- html.entities — HTML 一般实体的定义
- XML处理模块
- xml.etree.ElementTree — The ElementTree XML API
- xml.dom — The Document Object Model API
- xml.dom.minidom — Minimal DOM implementation
- xml.dom.pulldom — Support for building partial DOM trees
- xml.sax — Support for SAX2 parsers
- xml.sax.handler — Base classes for SAX handlers
- xml.sax.saxutils — SAX Utilities
- xml.sax.xmlreader — Interface for XML parsers
- xml.parsers.expat — Fast XML parsing using Expat
- 互联网协议和支持
- webbrowser — 方便的Web浏览器控制器
- cgi — Common Gateway Interface support
- cgitb — Traceback manager for CGI scripts
- wsgiref — WSGI Utilities and Reference Implementation
- urllib — URL 处理模块
- urllib.request — 用于打开 URL 的可扩展库
- urllib.response — Response classes used by urllib
- urllib.parse — Parse URLs into components
- urllib.error — Exception classes raised by urllib.request
- urllib.robotparser — Parser for robots.txt
- http — HTTP 模块
- http.client — HTTP协议客户端
- ftplib — FTP protocol client
- poplib — POP3 protocol client
- imaplib — IMAP4 protocol client
- nntplib — NNTP protocol client
- smtplib —SMTP协议客户端
- smtpd — SMTP Server
- telnetlib — Telnet client
- uuid — UUID objects according to RFC 4122
- socketserver — A framework for network servers
- http.server — HTTP 服务器
- http.cookies — HTTP state management
- http.cookiejar — Cookie handling for HTTP clients
- xmlrpc — XMLRPC 服务端与客户端模块
- xmlrpc.client — XML-RPC client access
- xmlrpc.server — Basic XML-RPC servers
- ipaddress — IPv4/IPv6 manipulation library
- 多媒体服务
- audioop — Manipulate raw audio data
- aifc — Read and write AIFF and AIFC files
- sunau — 读写 Sun AU 文件
- wave — 读写WAV格式文件
- chunk — Read IFF chunked data
- colorsys — Conversions between color systems
- imghdr — 推测图像类型
- sndhdr — 推测声音文件的类型
- ossaudiodev — Access to OSS-compatible audio devices
- 国际化
- gettext — 多语种国际化服务
- locale — 国际化服务
- 程序框架
- turtle — 海龟绘图
- cmd — 支持面向行的命令解释器
- shlex — Simple lexical analysis
- Tk图形用户界面(GUI)
- tkinter — Tcl/Tk的Python接口
- tkinter.ttk — Tk themed widgets
- tkinter.tix — Extension widgets for Tk
- tkinter.scrolledtext — 滚动文字控件
- IDLE
- 其他图形用户界面（GUI）包
- 开发工具
- typing — 类型标注支持
- pydoc — Documentation generator and online help system
- doctest — Test interactive Python examples
- unittest — 单元测试框架
- unittest.mock — mock object library
- unittest.mock 上手指南
- 2to3 - 自动将 Python 2 代码转为 Python 3 代码
- test — Regression tests package for Python
- test.support — Utilities for the Python test suite
- test.support.script_helper — Utilities for the Python execution tests
- 调试和分析
- bdb — Debugger framework
- faulthandler — Dump the Python traceback
- pdb — The Python Debugger
- The Python Profilers
- timeit — 测量小代码片段的执行时间
- trace — Trace or track Python statement execution
- tracemalloc — Trace memory allocations
- 软件打包和分发
- distutils — 构建和安装 Python 模块
- ensurepip — Bootstrapping the pip installer
- venv — 创建虚拟环境
- zipapp — Manage executable Python zip archives
- Python运行时服务
- sys — 系统相关的参数和函数
- sysconfig — Provide access to Python's configuration information
- builtins — 内建对象
- main — 顶层脚本环境
- warnings — Warning control
- dataclasses — 数据类
- contextlib — Utilities for with-statement contexts
- abc — 抽象基类
- atexit — 退出处理器
- traceback — Print or retrieve a stack traceback
- future — Future 语句定义
- gc — 垃圾回收器接口
- inspect — 检查对象
- site — Site-specific configuration hook
- 自定义 Python 解释器
- code — Interpreter base classes
- codeop — Compile Python code
- 导入模块
- zipimport — Import modules from Zip archives
- pkgutil — Package extension utility
- modulefinder — 查找脚本使用的模块
- runpy — Locating and executing Python modules
- importlib — The implementation of import
- Python 语言服务
- parser — Access Python parse trees
- ast — 抽象语法树
- symtable — Access to the compiler's symbol tables
- symbol — 与 Python 解析树一起使用的常量
- token — 与Python解析树一起使用的常量
- keyword — 检验Python关键字
- tokenize — Tokenizer for Python source
- tabnanny — 模糊缩进检测
- pyclbr — Python class browser support
- py_compile — Compile Python source files
- compileall — Byte-compile Python libraries
- dis — Python 字节码反汇编器
- pickletools — Tools for pickle developers
- 杂项服务
- formatter — Generic output formatting
- Windows系统相关模块
- msilib — Read and write Microsoft Installer files
- msvcrt — Useful routines from the MS VC++ runtime
- winreg — Windows 注册表访问
- winsound — Sound-playing interface for Windows
- Unix 专有服务
- posix — The most common POSIX system calls
- pwd — 用户密码数据库
- spwd — The shadow password database
- grp — The group database
- crypt — Function to check Unix passwords
- termios — POSIX style tty control
- tty — 终端控制功能
- pty — Pseudo-terminal utilities
- fcntl — The fcntl and ioctl system calls
- pipes — Interface to shell pipelines
- resource — Resource usage information
- nis — Interface to Sun's NIS (Yellow Pages)
- Unix syslog 库例程
- 被取代的模块
- optparse — Parser for command line options
- imp — Access the import internals
- 未创建文档的模块
- 平台特定模块
- 扩展和嵌入 Python 解释器
- 推荐的第三方工具
- 不使用第三方工具创建扩展
- 使用 C 或 C++ 扩展 Python
- 自定义扩展类型：教程
- 定义扩展类型：已分类主题
- 构建C/C++扩展
- 在Windows平台编译C和C++扩展
- 在更大的应用程序中嵌入 CPython 运行时
- Embedding Python in Another Application
- Python/C API 参考手册
- 概述
- 代码标准
- 包含文件
- 有用的宏
- 对象、类型和引用计数
- 异常
- 嵌入Python
- 调试构建
- 稳定的应用程序二进制接口
- The Very High Level Layer
- Reference Counting
- 异常处理
- Printing and clearing
- 抛出异常
- Issuing warnings
- Querying the error indicator
- Signal Handling
- Exception Classes
- Exception Objects
- Unicode Exception Objects
- Recursion Control
- 标准异常
- 标准警告类别
- 工具
- 操作系统实用程序
- 系统功能
- 过程控制
- 导入模块
- Data marshalling support
- 语句解释及变量编译
- 字符串转换与格式化
- 反射
- 编解码器注册与支持功能
- 抽象对象层
- Object Protocol
- 数字协议
- Sequence Protocol
- Mapping Protocol
- 迭代器协议
- 缓冲协议
- Old Buffer Protocol
- 具体的对象层
- 基本对象
- 数值对象
- 序列对象
- 容器对象
- 函数对象
- 其他对象
- Initialization, Finalization, and Threads
- 在Python初始化之前
- 全局配置变量
- Initializing and finalizing the interpreter
- Process-wide parameters
- Thread State and the Global Interpreter Lock
- Sub-interpreter support
- Asynchronous Notifications
- Profiling and Tracing
- Advanced Debugger Support
- Thread Local Storage Support
- 内存管理
- 概述
- 原始内存接口
- Memory Interface
- 对象分配器
- 默认内存分配器
- Customize Memory Allocators
- The pymalloc allocator
- tracemalloc C API
- 示例
- 对象实现支持
- 在堆中分配对象
- Common Object Structures
- Type 对象
- Number Object Structures
- Mapping Object Structures
- Sequence Object Structures
- Buffer Object Structures
- Async Object Structures
- 使对象类型支持循环垃圾回收
- API 和 ABI 版本管理
- 分发 Python 模块
- 关键术语
- 开源许可与协作
- 安装工具
- 阅读指南
- 我该如何...？
- ...为我的项目选择一个名字？
- ...创建和分发二进制扩展？
- 安装 Python 模块
- 关键术语
- 基本使用
- 我应如何 ...？
- ... 在 Python 3.4 之前的 Python 版本中安装 pip ？
- ... 只为当前用户安装软件包？
- ... 安装科学计算类 Python 软件包？
- ... 使用并行安装的多个 Python 版本？
- 常见的安装问题
- 在 Linux 的系统 Python 版本上安装
- 未安装 pip
- 安装二进制编译扩展
- Python 常用指引
- 将 Python 2 代码迁移到 Python 3
- 简要说明
- 详情
- 将扩展模块移植到 Python 3
- 条件编译
- 对象API的更改
- 模块初始化和状态
- CObject 替换为 Capsule
- 其他选项
- Curses Programming with Python
- What is curses?
- Starting and ending a curses application
- Windows and Pads
- Displaying Text
- User Input
- For More Information
- 实现描述器
- 摘要
- 定义和简介
- 描述器协议
- 发起调用描述符
- 描述符示例
- Properties
- 函数和方法
- Static Methods and Class Methods
- 函数式编程指引
- 概述
- 迭代器
- 生成器表达式和列表推导式
- 生成器
- 内置函数
- itertools 模块
- The functools module
- Small functions and the lambda expression
- Revision History and Acknowledgements
- 引用文献
- 日志 HOWTO
- 日志基础教程
- 进阶日志教程
- 日志级别
- 有用的处理程序
- 记录日志中引发的异常
- 使用任意对象作为消息
- 优化
- 日志操作手册
- 在多个模块中使用日志
- 在多线程中使用日志
- 使用多个日志处理器和多种格式化
- 在多个地方记录日志
- 日志服务器配置示例
- 处理日志处理器的阻塞
- Sending and receiving logging events across a network
- Adding contextual information to your logging output
- Logging to a single file from multiple processes
- Using file rotation
- Use of alternative formatting styles
- Customizing LogRecord
- Subclassing QueueHandler - a ZeroMQ example
- Subclassing QueueListener - a ZeroMQ example
- An example dictionary-based configuration
- Using a rotator and namer to customize log rotation processing
- A more elaborate multiprocessing example
- Inserting a BOM into messages sent to a SysLogHandler
- Implementing structured logging
- Customizing handlers with dictConfig()
- Using particular formatting styles throughout your application
- Configuring filters with dictConfig()
- Customized exception formatting
- Speaking logging messages
- Buffering logging messages and outputting them conditionally
- Formatting times using UTC (GMT) via configuration
- Using a context manager for selective logging
- 正则表达式HOWTO
- 概述
- 简单模式
- 使用正则表达式
- 更多模式能力
- 修改字符串
- 常见问题
- 反馈
- 套接字编程指南
- 套接字
- 创建套接字
- 使用一个套接字
- 断开连接
- 非阻塞的套接字
- 排序指南
- 基本排序
- 关键函数
- Operator 模块函数
- 升序和降序
- 排序稳定性和排序复杂度
- 使用装饰-排序-去装饰的旧方法
- 使用 cmp 参数的旧方法
- 其它
- Unicode 指南
- Unicode 概述
- Python's Unicode Support
- Reading and Writing Unicode Data
- Acknowledgements
- 如何使用urllib包获取网络资源
- 概述
- Fetching URLs
- 处理异常
- info and geturl
- Openers and Handlers
- Basic Authentication
- Proxies
- Sockets and Layers
- 脚注
- Argparse 教程
- 概念
- 基础
- 位置参数介绍
- Introducing Optional arguments
- Combining Positional and Optional arguments
- Getting a little more advanced
- Conclusion
- ipaddress模块介绍
- 创建 Address/Network/Interface 对象
- 审查 Address/Network/Interface 对象
- Network 作为 Address 列表
- 比较
- 将IP地址与其他模块一起使用
- 实例创建失败时获取更多详细信息
- Argument Clinic How-To
- The Goals Of Argument Clinic
- Basic Concepts And Usage
- Converting Your First Function
- Advanced Topics
- 使用 DTrace 和 SystemTap 检测CPython
- Enabling the static markers
- Static DTrace probes
- Static SystemTap markers
- Available static markers
- SystemTap Tapsets
- 示例
- Python 常见问题
- Python常见问题
- 一般信息
- 现实世界中的 Python
- 编程常见问题
- 一般问题
- 核心语言
- 数字和字符串
- 性能
- 序列（元组/列表）
- 对象
- 模块
- 设计和历史常见问题
- 为什么Python使用缩进来分组语句？
- 为什么简单的算术运算得到奇怪的结果？
- 为什么浮点计算不准确？
- 为什么Python字符串是不可变的？
- 为什么必须在方法定义和调用中显式使用“self”？
- 为什么不能在表达式中赋值？
- 为什么Python对某些功能（例如list.index()）使用方法来实现，而其他功能（例如len(List)）使用函数实现？
- 为什么 join()是一个字符串方法而不是列表或元组方法？
- 异常有多快？
- 为什么Python中没有switch或case语句？
- 难道不能在解释器中模拟线程，而非得依赖特定于操作系统的线程实现吗？
- 为什么lambda表达式不能包含语句？
- 可以将Python编译为机器代码，C或其他语言吗？
- Python如何管理内存？
- 为什么CPython不使用更传统的垃圾回收方案？
- CPython退出时为什么不释放所有内存？
- 为什么有单独的元组和列表数据类型？
- 列表是如何在CPython中实现的？
- 字典是如何在CPython中实现的？
- 为什么字典key必须是不可变的？
- 为什么 list.sort() 没有返回排序列表？
- 如何在Python中指定和实施接口规范？
- 为什么没有goto？
- 为什么原始字符串（r-strings）不能以反斜杠结尾？
- 为什么Python没有属性赋值的“with”语句？
- 为什么 if/while/def/class语句需要冒号？
- 为什么Python在列表和元组的末尾允许使用逗号？
- 代码库和插件 FAQ
- 通用的代码库问题
- 通用任务
- 线程相关
- 输入输出
- 网络 / Internet 编程
- 数据库
- 数学和数字
- 扩展/嵌入常见问题
- 可以使用C语言中创建自己的函数吗？
- 可以使用C++语言中创建自己的函数吗？
- C很难写，有没有其他选择？
- 如何从C执行任意Python语句？
- 如何从C中评估任意Python表达式？
- 如何从Python对象中提取C的值？
- 如何使用Py_BuildValue()创建任意长度的元组？
- 如何从C调用对象的方法？
- 如何捕获PyErr_Print()（或打印到stdout / stderr的任何内容）的输出？
- 如何从C访问用Python编写的模块？
- 如何从Python接口到C ++对象？
- 我使用Setup文件添加了一个模块，为什么make失败了？
- 如何调试扩展？
- 我想在Linux系统上编译一个Python模块，但是缺少一些文件。为什么?
- 如何区分“输入不完整”和“输入无效”？
- 如何找到未定义的g++符号__builtin_new或__pure_virtual？
- 能否创建一个对象类，其中部分方法在C中实现，而其他方法在Python中实现（例如通过继承）？
- Python在Windows上的常见问题
- 我怎样在Windows下运行一个Python程序？
- 我怎么让 Python 脚本可执行？
- 为什么有时候 Python 程序会启动缓慢？
- 我怎样使用Python脚本制作可执行文件？
- *.pyd 文件和DLL文件相同吗？
- 我怎样将Python嵌入一个Windows程序？
- 如何让编辑器不要在我的 Python 源代码中插入 tab ？
- 如何在不阻塞的情况下检查按键？
- 图形用户界面（GUI）常见问题
- 图形界面常见问题
- Python 是否有平台无关的图形界面工具包？
- 有哪些Python的GUI工具是某个平台专用的？
- 有关Tkinter的问题
- “为什么我的电脑上安装了 Python ？”
- 什么是Python？
- 为什么我的电脑上安装了 Python ？
- 我能删除 Python 吗？
- 术语对照表
- 文档说明
- Python 文档贡献者
- 解决 Bug
- 文档错误
- 使用 Python 的错误追踪系统
- 开始为 Python 贡献您的知识
- 版权
- 历史和许可证
- 软件历史
- 访问Python或以其他方式使用Python的条款和条件
- Python 3.7.3 的 PSF 许可协议
- Python 2.0 的 BeOpen.com 许可协议
- Python 1.6.1 的 CNRI 许可协议
- Python 0.9.0 至 1.2 的 CWI 许可协议
- 集成软件的许可和认可
- Mersenne Twister
- 套接字
- Asynchronous socket services
- Cookie management
- Execution tracing
- UUencode and UUdecode functions
- XML Remote Procedure Calls
- test_epoll
- Select kqueue
- SipHash24
- strtod and dtoa
- OpenSSL
- expat
- libffi
- zlib
- cfuhash
- libmpdec