I have a question which seems to be rather fundamental but I can't seem to find any help on this anywhere.
file_a.py >> from xyz import XYZ class A: . . . file_b.py >> import file_a from file_a import A class B(A): def __init__(self): A.__init__(self) def someMethod(self): XYZ.doSomething()
XYZ.doSomething() fails saying NameError: name 'XYZ' is not defined Even standard imports like 'import sys' done from file_a does not seem to render it usable in file_b. I assumed that should work. Is my understanding wrong? If yes, then is there a way to have common imports and global variables across files? (If it is of nay help, I've been a C++ and java programmer and am now starting to use python. )
Is my understanding wrong?
Yes, because the line
from file_a import A import only class
A into the namespace of
file_b. The namespace of
file_a is left alone. If it were not like this, there would be little sense in having both syntax:
import modulename from modulename import something
as if your thinking was right, then after the second form you would always be able to use
If yes, then is there a way to have common imports and global variables across files?
Yes, with the star
from modulename import *
but this brings the issue of namespace pollution, for example
from file_a import * will import in
file_b also all the imports done in
file_a. You will eventually lose control of your imports and this will bite you at some time... trust me on this!
When for some reason
from module import * is needed, a workaround to namespace pollution is to define in
module the variable
__all__, which whitelists what should be imported with the star operator.