数据解析时，python可以相互转换各种数据类型。最近在斯坦福公开课《密码学》网站上面做题发现，我对数据转换很不熟悉，写下日志记下用法。
导航
| | 数字 | 字符串 | 字节码 |
| --- | --- | --- | --- |
| 到数字 | [进制转换](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#进制转换) | [字符转整数](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#字符to整数) | [字节串转整数](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#字节串to整数) |
| 到字符串 | str() | [字符串编码解码](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#字节串to字符串) | decode(‘hex’) |
| 到字节码 | [数字转字符串](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#整数to字节串) | [字符串转字节串](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#字符串to字节串) | no |
还有常见的单个字符转换
| 函数 | 功能 | 记忆口诀 | 备注 |
| --- | --- | --- | --- |
| chr | 数字转成对应的ascii字符 | chr长得很像char，因此转成char | 范围为0~255 |
| ord | 单个字符转对应ascii序号 | digit为最后一个字母 |
### [](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#进制转换 "进制转换")进制转换
10进制转16进制:
~~~
hex(16) ==> 0x10
~~~
16进制转10进制:
int(STRING,BASE)将字符串STRING转成十进制int，其中STRING的基是base。该函数的第一个参数是字符串
~~~
int('0x10', 16) ==> 16
~~~
类似的还有八进制oct()， 二进制bin()
16进制字符串转成二进制
~~~
hex_str='00fe'
bin(int('1'+hex_str, 16))[3:] #含有前导0
# 结果 '0000000011111110'
bin(int(hex_str, 16))[2:] #忽略前导0
# 结果 '11111110'
~~~
二进制字符串转成16进制字符串
~~~
bin_str='0b0111000011001100'
hex(int(bin_str,2))
# 结果 '0x70cc'
~~~
### [](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#字符to整数 "字符to整数")字符to整数
10进制字符串:
~~~
int('10') ==> 10
~~~
16进制字符串:
~~~
int('10', 16) ==> 16
# 或者
int('0x10', 16) ==> 16
~~~
### [](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#字节串to整数 "字节串to整数")字节串to整数
使用网络数据包常用的struct，兼容C语言的数据结构
struct中支持的格式如下表
| Format | C-Type | Python-Type | 字节数 | 备注 |
| --- | --- | --- | --- | --- |
| x | pad byte | no value | 1 | |
| c | char | string of length 1 | 1 | |
| b | signed char | integer | 1 | |
| B | unsigned char | integer | 1 | |
| ? | _Bool | bool | 1 | |
| h | short | integer | 2 | |
| H | unsigned short | integer | 2 | |
| i | int | integer | 4 | |
| I | unsigned int | integer or long | 4 | |
| l | long | integer | 4 | |
| L | unsigned long | long | 4 | |
| q | long long | long | 8 | 仅支持64bit机器 |
| Q | unsigned long long | long | 8 | 仅支持64bit机器 |
| f | float | float | 4 | |
| d | double | float | 8 | |
| s | char[] | string | 1 | |
| p | char[] | string | 1(与机器有关) | 作为指针 |
| P | void * | long | 4 | 作为指针 |
对齐方式：放在第一个fmt位置
| CHARACTER | BYTE ORDER | SIZE | ALIGNMENT |
| --- | --- | --- | --- |
| @ | native | native | native |
| = | native | standard | none |
| < | little-endian | standard | none |
| > | big-endian | standard | none |
| ! | network (= big-endian) | standard | none |
转义为short型整数:
~~~
struct.unpack('<hh', bytes(b'\x01\x00\x00\x00')) ==> (1, 0)
~~~
转义为long型整数:
~~~
struct.unpack('<L', bytes(b'\x01\x00\x00\x00')) ==> (1,)
~~~
### [](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#整数to字节串 "整数to字节串")整数to字节串
转为两个字节:
~~~
struct.pack('<HH', 1,2) ==> b'\x01\x00\x02\x00'
~~~
转为四个字节:
~~~
struct.pack('<LL', 1,2) ==> b'\x01\x00\x00\x00\x02\x00\x00\x00'
~~~
### [](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#整数to字符串 "整数to字符串")整数to字符串
直接用函数
~~~
str(100)
~~~
### [](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#字符串to字节串 "字符串to字节串")字符串to字节串
[我用c++实现的encode(hex)和decode(hex)](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#CPP实现encode)
*decode和encode区别*
decode函数是重新解码，把CT字符串所显示的69dda8455c7dd425【每隔两个字符】解码成十六进制字符\x69\xdd\xa8\x45\x5c\x7d\xd4\x25
~~~
CT='69dda8455c7dd425'
print "%r"%CT.decode('hex')
~~~
encode函数是重新编码，把CT字符串所显示的69dda8455c7dd425【每个字符】编码成acsii值，ascii值为十六进制显示，占两位。执行下列结果显示36396464613834353563376464343235等价于将CT第一个字符’6’编码为0x36h 第二个字符’9’编码为0x39h
~~~
CT='69dda8455c7dd425'
print "%r"%CT.encode('hex')
~~~
*可以理解为：decode解码，字符串变短一半，encode编码，字符串变为两倍长度*
decode(‘ascii’)解码为字符串Unicode格式。输出带有’u’
encode(‘ascii’)，编码为Unicode格式，其实python默认处理字符串存储就是Unicode，输出结果估计和原来的字符串一样。
字符串编码为字节码:
~~~
'12abc'.encode('ascii') ==> b'12abc'
~~~
数字或字符数组:
~~~
bytes([1,2, ord('1'),ord('2')]) ==> b'\x01\x0212'
~~~
16进制字符串:
~~~
bytes().fromhex('010210') ==> b'\x01\x02\x10'
~~~
16进制字符串:
~~~
bytes(map(ord, '\x01\x02\x31\x32')) ==> b'\x01\x0212'
~~~
16进制数组:
~~~
bytes([0x01,0x02,0x31,0x32]) ==> b'\x01\x0212'
~~~
### [](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#字节串to字符串 "字节串to字符串")字节串to字符串
字节码解码为字符串:
~~~
bytes(b'\x31\x32\x61\x62').decode('ascii') ==> 12ab
~~~
字节串转16进制表示,夹带ascii:
~~~
str(bytes(b'\x01\x0212'))[2:-1] ==> \x01\x0212
~~~
字节串转16进制表示,固定两个字符表示:
~~~
str(binascii.b2a_hex(b'\x01\x0212'))[2:-1] ==> 01023132
~~~
字节串转16进制数组:
~~~
[hex(x) for x in bytes(b'\x01\x0212')] ==> ['0x1', '0x2', '0x31', '0x32']
~~~
问题：什么时候字符串前面加上’r’、’b’、’r’，其实官方文档有写。我认为在Python2中，r和b是等效的。
The Python 2.x documentation:
> A prefix of ‘b’ or ‘B’ is ignored in Python 2; it indicates that the literal should become a bytes literal in Python 3 (e.g. when code is automatically converted with 2to3). A ‘u’ or ‘b’ prefix may be followed by an ‘r’ prefix.
> ‘b’字符加在字符串前面，对于python2会被忽略。加上’b’目的仅仅为了兼容python3，让python3以bytes数据类型(0~255)存放这个字符、字符串。
The Python 3.3 documentation states:
> Bytes literals are always prefixed with ‘b’ or ‘B’; they produce an instance of the bytes type instead of the str type. They may only contain ASCII characters; bytes with a numeric value of 128 or greater must be expressed with escapes.
> 数据类型byte总是以’b’为前缀，该数据类型仅为ascii。
下面是stackflow上面一个回答。我觉得不错，拿出来跟大家分享
In Python 2.x
> Pre-3.0 versions of Python lacked this kind of distinction between text and binary data. Instead, there was:
>
> * unicode = u’…’ literals = sequence of Unicode characters = 3.x str
> * str = ‘…’ literals = sequences of confounded bytes/characters
> Usually text, encoded in some unspecified encoding.
> But also used to represent binary data like struct.pack output.
Python 3.x makes a clear distinction between the types:
> * str = ‘…’ literals = a sequence of Unicode characters (UTF-16 or UTF-32, depending on how Python was compiled)
> * bytes = b’…’ literals = a sequence of octets (integers between 0 and 255)
### [](https://lixingcong.github.io/2016/03/06/convert-data-in-python/#CPP实现encode "CPP实现encode")CPP实现encode
就是做个笔记，毕竟在做题Cryptography时候用c++写字符串的处理很蛋疼！为了防止再次造轮子，记下来。
~~~
#include <cstring> //用到strlen函数
static unsigned char ByteMap[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8','9', 'a', 'b', 'c', 'd', 'e', 'f' };
unsigned char hex_2_dec(unsigned char c){
if(c >= '0' && c <= '9') return c - '0';
if(c >= 'a' && c <= 'f') return c - 'a' + 10;
}
void str_encode(unsigned char *src, unsigned char *dest, int len_of_src) {
// 使用注意：dest_len >= 2*len_src +1，最后一位是存放'\0'。
int t1;
for (int i = 0; i < len_of_src; ++i) {
t1 = (int) src[i];
dest[2 * i] = ByteMap[t1 / 16];
dest[2 * i + 1] = ByteMap[t1 % 16];
}
dest[2 * len_of_src] = 0; //必须填充最后一个为'\0'
}
void str_decode(unsigned char *src,unsigned char *dest){
int len_of_src=strlen((char *)src);
unsigned char t1;
for(int i=1;i<=len_of_src;i+=2){
t1=hex_2_dec(src[i-1]);
t1= 16*t1 + hex_2_dec(src[i]);
dest[i/2]=t1;
}
}
~~~
鸣谢
本文转载自csdn博客的[《python常用的十进制、16进制、字符串、字节串之间的转换》](http://blog.csdn.net/crylearner/article/details/38521685)。
- 空白目录
- serial
- serial 整理
- hex to str
- Python3 字符编码
- 字符串编码与Python 3编码
- python3中bytes和string之间的互相转换
- Python3 字符编码
- python整数、字符串、字节串相互转换
- python整数、字符串、字节串相互转换
- python常用的十进制、16进制、字符串、字节串之间的转换（长期更新帖）
- python中pyserial模块使用方法
- 谈谈 Python 程序的运行原理
- flask
- Flask 在 Debug 模式下初始化2次
- Flask中向前端传递或者接收Json文件的方法
- 使用 Python 和 Flask 设计 RESTful API
- 使用 Flask-RESTful 设计 RESTful API