python整數、字符串、字節串相互轉換 · python

[TOC] python的數據轉換很靈活，所以用日志記錄下他們的用法。 ### 概覽 | | 數字 | 字符串 | 字節碼 | | --- | --- | --- | --- | | 到數字 | [進制轉換](https://edonymu.com/2017/06/18/python%E6%95%B4%E6%95%B0%E3%80%81%E5%AD%97%E7%AC%A6%E4%B8%B2%E3%80%81%E5%AD%97%E8%8A%82%E4%B8%B2%E7%9B%B8%E4%BA%92%E8%BD%AC%E6%8D%A2/#進制轉換) | [字符轉整數](https://edonymu.com/2017/06/18/python%E6%95%B4%E6%95%B0%E3%80%81%E5%AD%97%E7%AC%A6%E4%B8%B2%E3%80%81%E5%AD%97%E8%8A%82%E4%B8%B2%E7%9B%B8%E4%BA%92%E8%BD%AC%E6%8D%A2/#字符to整數) | [字節串轉整數](https://edonymu.com/2017/06/18/python%E6%95%B4%E6%95%B0%E3%80%81%E5%AD%97%E7%AC%A6%E4%B8%B2%E3%80%81%E5%AD%97%E8%8A%82%E4%B8%B2%E7%9B%B8%E4%BA%92%E8%BD%AC%E6%8D%A2/#字節串to整數) | | 到字符串 | str() | [字符串編碼解碼](https://edonymu.com/2017/06/18/python%E6%95%B4%E6%95%B0%E3%80%81%E5%AD%97%E7%AC%A6%E4%B8%B2%E3%80%81%E5%AD%97%E8%8A%82%E4%B8%B2%E7%9B%B8%E4%BA%92%E8%BD%AC%E6%8D%A2/#字節串to字符串) | decode(‘hex’) | | 到字節碼 | [數字轉字符串](https://edonymu.com/2017/06/18/python%E6%95%B4%E6%95%B0%E3%80%81%E5%AD%97%E7%AC%A6%E4%B8%B2%E3%80%81%E5%AD%97%E8%8A%82%E4%B8%B2%E7%9B%B8%E4%BA%92%E8%BD%AC%E6%8D%A2/#整數to字節串) | [字符串轉字節串](https://edonymu.com/2017/06/18/python%E6%95%B4%E6%95%B0%E3%80%81%E5%AD%97%E7%AC%A6%E4%B8%B2%E3%80%81%E5%AD%97%E8%8A%82%E4%B8%B2%E7%9B%B8%E4%BA%92%E8%BD%AC%E6%8D%A2/#字符串to字節串) | no | | 函數 | 功能 | 記憶口訣 | 備注 | | --- | --- | --- | --- | | chr | 數字轉成對應的ascii字符 | chr長得很像char，因此轉成char | 范圍為0~255 | | ord | 單個字符轉對應ascii序號 | digit為最后一個字母 | ### 進制轉換 * 10進制轉16進制: ~~~ hex(16) ==> 0x10 ~~~ * 16進制轉10進制: int(STRING,BASE)將字符串STRING轉成十進制int，其中STRING的基是base。該函數的第一個參數是字符串 ~~~ int('0x10', 16) ==> 16 ~~~ 類似的還有八進制oct()，二進制bin() * 16進制字符串轉成二進制 ~~~ hex_str='00fe' bin(int('1'+hex_str, 16))[3:] #含有前導0 # 結果 '0000000011111110' bin(int(hex_str, 16))[2:] #忽略前導0 # 結果 '11111110' ~~~ * 二進制字符串轉成16進制字符串 ~~~ bin_str='0b0111000011001100' hex(int(bin_str,2)) # 結果 '0x70cc' ~~~ ### 字符to整數 * 10進制字符串: ~~~ int('10') ==> 10 ~~~ * 16進制字符串: ~~~ int('10', 16) ==> 16 # 或者 int('0x10', 16) ==> 16 ~~~ * 字節串to整數使用網絡數據包常用的struct，兼容C語言的數據結構 struct中支持的格式如下表 | Format | C-Type | Python-Type | 字節數 | 備注 | | --- | --- | --- | --- | --- | | 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 | 僅支持64bit機器 | | Q | unsigned long long | long | 8 | 僅支持64bit機器 | | f | float | float | 4 | | | d | double | float | 8 | | | s | char[] | string | 1 | | | p | char[] | string | 1(與機器有關) | 作為指針 | | P | void * | long | 4 | 作為指針 | 對齊方式：放在第一個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 | * 轉義為short型整數: ~~~ struct.unpack(' (1, 0) ~~~ * 轉義為long型整數: ~~~ struct.unpack(' (1,) ~~~ ### 整數to字節串 * 轉為兩個字節: ~~~ struct.pack(' b'\x01\x00\x02\x00' ~~~ * 轉為四個字節: ~~~ struct.pack(' b'\x01\x00\x00\x00\x02\x00\x00\x00' ~~~ ### 整數to字符串 * 直接用函數 ~~~ str(100) ~~~ ### 字符串to字節串 * bytes、str與unicode的區別 Python3有兩種表示字符序列的類型：bytes和str。前者的實例包含原始的8位值，后者的實例包含Unicode字符。 Python2也有兩種表示字符序列的類型，分別叫做str和Unicode。與Python3不同的是，str實例包含原始的8位值；而unicode的實例，則包含Unicode字符。把Unicode字符表示為二進制數據（也就是原始8位值）有許多種辦法。最常見的編碼方式就是UTF-8。但是，Python3的str實例和Python2的unicode實例都沒有和特定的二進制編碼形式相關聯。要想把Unicode字符轉換成二進制數據，就必須使用encode方法。要想把二進制數據轉換成Unicode字符，則必須使用decode方法。編寫Python程序的時候，一定要把編碼和解碼操作放在界面最外圍來做。程序的核心部分應該使用Unicode字符類型（也就是Python3中的str、Python2中的unicode），而且不要對字符編碼做任何假設。這種辦法既可以令程序接受多種類型的文本編碼（如Latin-1、Shift JIS和Big5），又可以保證輸出的文本信息只采用一種編碼形式（最好是UTF-8）。由于字符類型有別，所以Python代碼中經常會出現兩種常見的使用情境：開發者需要原始8位值，這些8位值表示以UTF-8格式（或其他編碼形式）來編碼的字符。開發者需要操作沒有特定編碼形式的Unicode字符。 * *decode和encode區別* ![python-str](https://edonymu.files.wordpress.com/2017/06/python-str.png?w=660) * 字符串編碼為字節碼: ~~~ '12abc'.encode('ascii') ==> b'12abc' ~~~ * 數字或字符數組: ~~~ bytes([1,2, ord('1'),ord('2')]) ==> b'\x01\x0212' ~~~ * 16進制字符串: ~~~ bytes().fromhex('010210') ==> b'\x01\x02\x10' ~~~ * 16進制字符串: ~~~ bytes(map(ord, '\x01\x02\x31\x32')) ==> b'\x01\x0212' ~~~ * 16進制數組: ~~~ bytes([0x01,0x02,0x31,0x32]) ==> b'\x01\x0212' ~~~ ### 字節串to字符串 * 字節碼解碼為字符串: ~~~ bytes(b'\x31\x32\x61\x62').decode('ascii') ==> 12ab ~~~ * 字節串轉16進制表示,夾帶ascii: ~~~ str(bytes(b'\x01\x0212'))[2:-1] ==> \x01\x0212 ~~~ * 字節串轉16進制表示,固定兩個字符表示: ~~~ str(binascii.b2a_hex(b'\x01\x0212'))[2:-1] ==> 01023132 ~~~ * 字節串轉16進制數組: ~~~ [hex(x) for x in bytes(b'\x01\x0212')] ==> ['0x1', '0x2', '0x31', '0x32'] ~~~ 問題：什么時候字符串前面加上’r’、’b’、’u’，其實官方文檔有寫。我認為在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，對于python2會被忽略。加上’b’目的僅僅為了兼容python3，讓python3以bytes數據類型(0~255)存放這個字符、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. > 數據類型byte總是以’b’為前綴，該數據類型僅為ascii。下面是stackflow上面一個回答。我覺得不錯，拿出來跟大家分享 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) [參考文獻](https://lixingcong.github.io/2016/03/06/convert-data-in-python/)