On 2012-08-08 06:14, Ben Finney wrote:
Cameron Simpson <c...@zip.com.au> writes:
All of you are saying "two names for the same module", and variations
thereof. And that is why the doco confuses.
I would expect less confusion if the above example were described as
_two_ modules, with the same source code.
That's not true though, is it? It's the same module object with two
different references, I thought.
They are not the same. Proof:
$ mkdir test
$ cd test
$ touch __init__.py
$ touch m.py
$ cd ..
$ python
Python 2.7.3 (default, Apr 20 2012, 22:39:59)
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.path.append('test')
>>> import m
>>> from test import m
>>> import m
>>> from test import m as m2
>>> m is m2
False
>>> m.a = 3
>>> m2.a
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'a'
So it is still true that top level code gets executed only once, when
the module is first imported. The trick is that a module is not a file.
It is a module object that is created from a file, with a name. If you
change the name, then you create ("import") a new module.
You can also use the reload() function to execute module level code
again, but it won't create a new module object. It will just update the
contents of the very same module object:
What is more interesting is how the reload() function works:
Python 2.7.3 (default, Apr 20 2012, 22:39:59)
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import test.m
>>> a = test.m
>>> import os
>>> test.m is a
True
>>> os.system("echo \"import sys\" >> test/m.py")
0
>>> reload(test.m) # Updates the module object
<module 'test.m' from 'test/m.py'>
>>> test.m is a # They are still the same
True
>>> a.sys # So a.sys is a exist
<module 'sys' (built-in)>
>>>
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