Does __import__ require a module to have a .py suffix?

Gabriel Genellina gagsl-py2 at
Wed Mar 19 03:37:15 CET 2008

En Wed, 12 Mar 2008 18:02:54 -0200, Jean-Paul Calderone  
<exarkun at> escribió:

> On Wed, 12 Mar 2008 12:58:33 -0700 (PDT), George Sakkis  
> <george.sakkis at> wrote:
>> On Mar 12, 12:22 pm, mrstephengross <mrstevegr... at> wrote:
>>> Hi all. I've got a python file called 'foo' (no extension). I want to
>>> be able to load it as a module, like so:
>>>   m = __import__('foo')
>> You can use execfile:
>> foo = {}
>> execfile('foo', foo)
>> Apart from the different syntax in accessing the module globals
>> (attributes with __import__ (foo.x) vs dict entries with execfile
>> (foo['x'])), there are probably more subtle differences but I can't
>> tell for sure. It would be nice if someone more knowledgeable can
>> compare and contrast these two appraches.
> Another difference is that when you import a module, its code is  
> (usually)
> only executed once.  Each import after the first just returns a reference
> to the already-created module object.  When you use execfile, the code is
> re-evaluated each time.

The steps done by import are outlined in this message
The relevant part (citing myself):

newmodule = sys.modules[modulename] = ModuleType(modulename)
# constructor sets __name__ and a null __doc__
newmodule.__builtins__ = current builtins
newmodule.__file__ = filename
code = read from filename and compile it
exec code in newmodule.__dict__

Apart from sys.modules and __file__, there is another difference, the  
__builtins__ attribute. It is important: if not present, Python executes  
the code in "safe mode" where certain operations are disabled (and there  
is a big performance penalty).

Gabriel Genellina

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