爲什麼Python的base64.b64decode（）在字符串結尾忽略亂碼？

我有一個很長的道理，我正在使用python的base64.b64decode()方法進行解碼。爲什麼Python的base64.b64decode（）在字符串結尾忽略亂碼？

它的工作原理。但是，如下所示，即使在最後插入亂碼字符，它也會返回相同的結果。爲什麼？這兩個字符串不應該產生兩個不同的解碼結果嗎？

>>> import base64 
>>> token = "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" 
>>> base64.b64decode("%sXXXXXXBlahBlahBlah" % (token)) == base64.b64decode(token) 
True

如果我把亂碼字符開頭，它失敗：

>>> base64.b64decode("%sXXXXXXBlahBlahBlah" % (token)) == base64.b64decode(token) 
Traceback (most recent call last): 
    File "<stdin>", line 1, in <module> 
    File "/usr/local/Cellar/python/2.7.8_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/base64.py", line 76, in b64decode 
    raise TypeError(msg) 
TypeError: Incorrect padding

來源

2016-05-02 Saqib Ali

@DisplayName：這會是' 「％sXXXXXXBlahBlahBlah」％（令牌）'。 – user2357112

糟糕。抱歉是。編輯。 –

The CPython implementation停止解釋，如果它看到一個墊（=）。

if (this_ch == BASE64_PAD) { 
     if ((quad_pos < 2) || 
      ((quad_pos == 2) && 
       (binascii_find_valid(ascii_data, ascii_len, 1) 
       != BASE64_PAD))) 
     { 
      continue; 
     } 
     else { 
      /* A pad sequence means no more input. 
      ** We've already interpreted the data 
      ** from the quad at this point. 
      */ 
      leftbits = 0; 
      break; 
     } 
    }

與base64編碼串的實驗沒有填充：

>>> base64.decodestring('YWJj') # without a padding 
'abc' 
>>> base64.decodestring('YWJj' + 'XXX') 
Traceback (most recent call last): 
    File "<stdin>", line 1, in <module> 
    File "/usr/lib/python2.7/base64.py", line 328, in decodestring 
    return binascii.a2b_base64(s) 
binascii.Error: Incorrect padding 

>>> base64.decodestring('YWI=') # with a padding 
'ab' 
>>> base64.decodestring('YWI=XXX') 
'ab'

來源

2016-05-02 07:45:38 falsetru

爲什麼Python的base64.b64decode（）在字符串結尾忽略亂碼？

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