[ python-Bugs-950057 ] itertools.chain doesn't "process" exceptions as they occur

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Bugs item #950057, was opened at 2004-05-07 20:32
Message generated for change (Comment added) made by mithrandi
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Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Tristan Seligmann (mithrandi)
>Assigned to: Raymond Hettinger (rhettinger)
Summary: itertools.chain doesn't "process" exceptions as they occur

Initial Comment:
Python 2.3.3 (#2, Feb 24 2004, 09:29:20)
[GCC 3.3.3 (Debian)] on linux2

The following code demonstrates the problem:

import itertools
                                                      
                                                      
                                               
def gen1():
    print 'Before yield 1'
    yield 1
    print 'After yield 1'
    assert False
                                                      
                                                      
                                               
def gen2(x = False):
    print 'Before yield 2'
    yield 2
    print 'After yield 2'
    if x:
        raise StopIteration
                                                      
                                                      
                                               
for elem in itertools.chain(gen1(), gen2()):
    print elem

The exception only propagates up after itertools.chain
completes iteration; if you pass True to gen2(), then
the AssertionError will be completely masked,
concealing the fact that any exception has been raised.

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>Comment By: Tristan Seligmann (mithrandi)
Date: 2004-05-07 20:34

Message:
Logged In: YES 
user_id=557968

Oops, providing example code as an attachment this time instead.

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