Doubley imported module caused devastating bug
ethan at stoneleaf.us
Thu Sep 24 21:51:23 CEST 2009
Zac Burns wrote:
> Currently it is possible to import a file of one path to more than one
> 'instance' of a module. One notable example is "import __init__" from
> a package. See http://stackoverflow.com/questions/436497/python-import-the-containing-package
> This recently caused a devastating bug in some of my code. What I have
> is support for the Perforce global options as a context for a perforce
> module. http://www.perforce.com/perforce/doc.072/manuals/cmdref/o.gopts.html#1040647
> This way one can call functions that call many perforce command and
> have them execute on a different client for example.
> So, in module A and module B both imported the Perforce module, but
> they turned out not to be the same module. Module A did "with
> Perforce.GlobalOptions(client=client): B.function()"
> B.function did not receive the new GlobalOptions because of this
> problem. As a result important files on the original client were
> overwritten (OUCH).
> I would like to propose that it be made impossible in the Python
> source to import two instances of the same module.
> Zachary Burns
> Aim - Zac256FL
> Production Engineer (Digital Overlord)
> Zindagi Games
I believe that modules are imported only once, and my toy example
demonstrates that (python 2.5):
"""testing multiple imports"""
CONSTANT = 928
version = (2, 0, 9)
plug_ins = 
random_text = 'some text here'
random_text = new_text
test_import.CONSTANT = 'changed!'
In : import A
(2, 0, 9)
In : import B
(2, 0, 9)
As you can see, module A made a change to test_import.CONSTANT, and if
they were different things then B would not have seen it, yet B *did*
This makes me wonder if A) Perforce.GlobalOptions isn't actually setting
module level variables, or B) B.function is using copies of those
variables that were set when B was originally imported, so is not seeing
the changes.... or C) there is yet another wrinkle here that I don't
know about. ;-)
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