with statement executes type(obj).__exit__ rather than getattr(obj,"__exit__")

[PaulWiseman]

BPO	16068

^{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 = None
closed_at = <Date 2012-09-28.03:10:23.129>
created_at = <Date 2012-09-28.03:02:34.436>
labels = ['invalid', 'type-bug', 'library']
title = 'with statement executes type(obj).__exit__ rather than getattr(obj,"__exit__")'
updated_at = <Date 2012-09-28.03:10:23.128>
user = 'https://bugs.python.org/PaulWiseman'

bugs.python.org fields:

activity = <Date 2012-09-28.03:10:23.128>
actor = 'Paul.Wiseman'
assignee = 'none'
closed = True
closed_date = <Date 2012-09-28.03:10:23.129>
closer = 'Paul.Wiseman'
components = ['Library (Lib)']
creation = <Date 2012-09-28.03:02:34.436>
creator = 'Paul.Wiseman'
dependencies = []
files = []
hgrepos = []
issue_num = 16068
keywords = []
message_count = 2.0
messages = ['171399', '171401']
nosy_count = 1.0
nosy_names = ['Paul.Wiseman']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue16068'
versions = ['Python 2.7']

[PaulWiseman]

I found this behaviour today and thought it was weird so asked the question on SO here http://stackoverflow.com/questions/12632894/why-doesnt-getattr-work-with-exit/12632972#12632972

basically if I attributes are returned dynamically, they seem to get overlooked by the code that runs the with statements.

>>> class FileHolder(object):
...    def __init__(self,*args,**kwargs):
...        self.f= file(*args,**kwargs)
...    def __getattr__(self,item):
...        return getattr(self.f,item)
...
>>> a= FileHolder("a","w")
>>> a.write
<built-in method write of file object at 0x018D75F8>
>>> with a as f:
...   print f
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: __exit__
>>> a.__exit__
<built-in method __exit__ of file object at 0x018D75F8>

[PaulWiseman]

I got pointed to an explanation in the docs! http://docs.python.org/reference/datamodel.html#special-method-lookup-for-new-style-classes

It was confusing, though :)