str.join() intercepts UnicodeDecodeError raised by iterator

[Cito]

BPO	1748292
Nosy	@malemburg, @doerwalter, @Cito

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/malemburg'
closed_at = <Date 2007-07-05.13:11:17.000>
created_at = <Date 2007-07-05.10:10:38.000>
labels = ['invalid', 'expert-unicode']
title = 'str.join() intercepts UnicodeDecodeError raised by iterator'
updated_at = <Date 2007-07-05.13:11:17.000>
user = 'https://github.com/Cito'

bugs.python.org fields:

activity = <Date 2007-07-05.13:11:17.000>
actor = 'cito'
assignee = 'lemburg'
closed = True
closed_date = None
closer = None
components = ['Unicode']
creation = <Date 2007-07-05.10:10:38.000>
creator = 'cito'
dependencies = []
files = []
hgrepos = []
issue_num = 1748292
keywords = []
message_count = 3.0
messages = ['32452', '32453', '32454']
nosy_count = 3.0
nosy_names = ['lemburg', 'doerwalter', 'cito']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1748292'
versions = ['Python 2.5']

[Cito]

This is somewhat similar to bpo-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

[doerwalter]

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()

[Cito]

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.