[Python-Dev] Rationale for NamedTemporaryFile?

[Aaron Bingham]

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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01307 Dresden, Germany
www.cenix-bioscience.com

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