New submission from Mark Dickinson <[email protected]>:
The following error message in Python 3.7 is confusing and unhelpful:
>>> s = "FS9qzW_oliGH_Yo="
>>> base64.b64decode(s)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/base64.py",
line 87, in b64decode
return binascii.a2b_base64(s)
binascii.Error: Invalid base64-encoded string: length cannot be 1 more than
a multiple of 4
>>> len(s) % 4
0
This had me staring at the string s and scratching my head, thinking: "s
doesn't have length 1 more than a multiple of 4, either with or without the "="
padding byte. What's this talking about?"
The actual user error here is a failure to use the "altchars" argument
correctly:
>>> base64.b64decode(s, altchars="-_")
b'\x15/j\xcdo\xe8\x96!\x87\xfd\x8a'
The error message in versions prior to Python 3.7 is no more helpful, but it's
not quite as misleading, either.
Python 3.6.6 (default, Jun 28 2018, 05:43:53)
[GCC 4.2.1 Compatible Apple LLVM 9.1.0 (clang-902.0.39.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import base64
>>> s = "FS9qzW_oliGH_Yo="
>>> base64.b64decode(s)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/base64.py",
line 87, in b64decode
return binascii.a2b_base64(s)
binascii.Error: Incorrect padding
Related: #1466065, #33770
----------
messages: 325757
nosy: mark.dickinson
priority: normal
severity: normal
status: open
title: Confusing base64.b64decode output
versions: Python 3.7
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Python tracker <[email protected]>
<https://bugs.python.org/issue34736>
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