[Python-Dev] Rationale for NamedTemporaryFile?

Wed Mar 21 18:25:15 CET 2007

Georg Brandl wrote:
> Aaron Bingham schrieb:
>>> Georg Brandl wrote:
>>>>> Greg Ewing schrieb:
>>>>>>>>>> Scott Dial wrote:
>>>>>>>> A tangential question -- why are TemporaryFile and
>>>> NamedTemporaryFile named in TitleCase, when they're
>>>> functions and not classes?
>>>>>>>>>>> Probably because they are factory functions potentially returning a
>>> _TemporaryFileWrapper. If they were "functions", they'd have to be
>>> verbed, e.g. "make_temporary_file()".
>>>>>> The class/function distinction is not so clear in Python from the user's
>>> point of view since there is no different calling syntax.
>>>>> Actually the distinction is very clear:
>>>> >>> class _PrivateClass(object):
>> ... pass
>> ...
>> >>> def FunctionNamedToLookLikeClass():
>> ... return _PrivateClass()
>> ...
>> >>> pc = _PrivateClass()
>> >>> isinstance(pc, _PrivateClass)
>> True
>> >>> fntllc = FunctionNamedToLookLikeClass()
>> >>> isinstance(fntllc, FunctionNamedToLookLikeClass)
>> Traceback (most recent call last):
>> File "<stdin>", line 1, in <module>
>> TypeError: isinstance() arg 2 must be a class, type, or tuple of classes 
>> and types
>>>> That's sure to be an unpleasant surprise for someone.
>>>> <whisper>duck typing...</whisper>
>> But you have a valid point.
>Sure, isinstance was only meant as an example. Anything that expects 
FunctionNamedToLookLikeClass to exhibit class-like behaviors beyond a 
call returning a new instance will fail.
-- 
Aaron Bingham
Senior Software Engineer
bingham at cenix-bioscience.com
Tel. +49 (0)351 4173-146
Fax +49 (0)351 4173-109
Cenix BioScience GmbH
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