[ python-Bugs-1748292 ] str.join() intercepts UnicodeDecodeError raised by iterator

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Bugs item #1748292, was opened at 2007-07-05 12:10
Message generated for change (Comment added) made by cito
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Category: Unicode
Group: Python 2.5
Status: Closed
Resolution: Invalid
Priority: 5
Private: No
Submitted By: Christoph Zwerschke (cito)
Assigned to: M.-A. Lemburg (lemburg)
Summary: str.join() intercepts UnicodeDecodeError raised by iterator

Initial Comment:
This is somewhat similar to #905389 which has already been fixed.

If you run the following two lines,

def gen(): raise UnicodeDecodeError
''.join(gen())

then instead of UnicodeDecodeError, you get:
TypeError: function takes exactly 5 arguments (0 given)

I found this bug in Python 2.3.5, 2.4.4 and 2.5.1 on Windows and Linux.

The bug appears exactly for UnicodeDecodeError,
UnicodeEncodeError, UnicodeTranslateError; all other exceptions work as expected. You can verify this with the following program:

import exceptions

def gen(e): raise e

for e in dir(exceptions):
    e = getattr(exceptions, e)
    if type(e) != type(Exception):
        continue
    try:
        ''.join(gen(e))
    except BaseException, f:
        e = e.__name__
        f = f.__class__.__name__
        if e != f:
            print e, f


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>Comment By: Christoph Zwerschke (cito)
Date: 2007-07-05 15:11

Message:
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user_id=193957
Originator: YES

Thanks for the quick analysis. You're completely right, it has nothing to
do with ''.join(). You get the same error if you simply

raise UnicodeDecodeError

which I think is a bit confusing nevertheless. I had naively assumed that
you can instantiate every Exception with no or a single string argument
only, so I did not consider this could be the cause. Sorry.

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Comment By: Walter Dörwald (doerwalter)
Date: 2007-07-05 13:07

Message:
Logged In: YES 
user_id=89016
Originator: NO

This has nothing to do with str.join(). The following script raises the
same exception:

def gen():
   raise UnicodeDecodeError()

gen()

The problem is exactly what the exception message states: the
UnicodeDecodeError constructor expects five arguments. The following
version raises the expected UnicodeDecodeError:

def gen():
   raise UnicodeDecodeError('ascii', 'bytes', 0, 1, 'ouch')
gen()


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