New submission from Nick Coghlan:
Passing the wrong types to codecs can currently lead to rather confusing
exceptions, like:
====================
>>> b"ZXhhbXBsZQ==\n".decode("base64_codec")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib64/python3.2/encodings/base64_codec.py", line 20, in
base64_decode
return (base64.decodebytes(input), len(input))
File "/usr/lib64/python3.2/base64.py", line 359, in decodebytes
raise TypeError("expected bytes, not %s" % s.__class__.__name__)
TypeError: expected bytes, not memoryview
====================
>>> codecs.decode("example", "utf8")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib64/python3.2/encodings/utf_8.py", line 16, in decode
return codecs.utf_8_decode(input, errors, True)
TypeError: 'str' does not support the buffer interface
====================
This situation could be improved by having the affected APIs use the exception
chaining system to wrap these errors in a more informative exception that also
display information on the codec involved. Note that UnicodeEncodeError and
UnicodeDecodeError are not appropriate, as those are specific to text encoding
operations, while these new wrappers will apply to arbitrary codecs, regardless
of whether or not they use the unicode error handlers. Furthermore, for
backwards compatibility with existing exception handling, it is probably
necessary to limit ourselves to specific exception types and ensure that the
wrapper exceptions are subclasses of those types.
These new wrappers would have __cause__ set to the exception raised by the
codec, but emit a message more along the lines of the following:
==============
codecs.DecodeTypeError: encoding='utf8', details="TypeError: 'str' does not
support the buffer interface"
==============
Wrapping TypeError and ValueError should cover most cases, which would mean
four new exception types in the codecs module:
Raised by codecs.decode, bytes.decode and bytearray.decode:
* codecs.DecodeTypeError
* codecs.DecodeValueError
Raised by codecs.encode, str.encode:
* codecs.EncodeTypeError
* codecs.EncodeValueError
Instances of UnicodeError wouldn't be wrapped, since they already contain codec
information.
----------
components: Library (Lib)
messages: 187704
nosy: ncoghlan
priority: normal
severity: normal
status: open
title: More informative error handling when encoding and decoding
versions: Python 3.4
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Python tracker <[email protected]>
<http://bugs.python.org/issue17828>
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