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
(407)590-4814
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):
test_import.py:
"""testing multiple imports"""
CONSTANT = 928
version = (2, 0, 9)
plug_ins = []
random_text = 'some text here'
def set_text(new_text):
global random_text
random_text = new_text
plug_ins.append(new_text)
A.py:
import test_import
print test_import.version
test_import.set_text('hello!')
print test_import.plug_ins
print test_import.CONSTANT
test_import.CONSTANT = 'changed!'
B.py:
import test_import
print test_import.version
test_import.set_text('world!')
print test_import.plug_ins
print test_import.CONSTANT
Running...
In [1]: import A
(2, 0, 9)
['hello!']
928
In [2]: import B
(2, 0, 9)
['hello!', 'world!']
changed!
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*
see it.
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. ;-)
~Ethan~
--
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