Classes and modules are singletons?

[Micah Cowan]

Steven D'Aprano <steve at REMOVE-THIS-cybersource.com.au> writes:

> I recall that Python guarantees that module objects are singletons, and 
> that this must hold for any implementation, not just CPython: you can 
> only ever create one instance of a module via the import mechanism. But 
> my google-foo is obviously weak today, I cannot find where the Python 
> language reference guarantees that. Can somebody please point me at the 
> link making that guarantee?


It's not an absolute strict guarantee; it's just implied by the fact
that "import" uses any appropriate objects already found in
sys.modules.

>>> import sys
>>> ll = []  
>>> for i in range(2):
...     import string
...     ll.append(string)
...     del sys.modules['string']
... 
>>> ll[0] is ll[1]
False

(I'm sure there are very good reasons never to do what I just did there.)

-- 
Micah J. Cowan
Programmer, musician, typesetting enthusiast, gamer...
http://micah.cowan.name/