I am finding a discrepancy I did not expect in the Python (3.8) example below.
We define a global variable in module config:
config.py:
global_variable = 80
Then two functions in module foo using that global variable in two different ways that I expected to be equivalent:
foo.py:
from config import global_variable
import config
def foo1():
return global_variable
def foo2():
return config.global_variable
Finally, I print the result of both functions after setting the global variable to 0 in a main script:
main.py:
import config
import foo
if __name__ == '__main__':
config.global_variable = 0
print("foo1(): ", foo.foo1())
print("foo2(): ", foo.foo2())
but I find them to have different results. The output is:
foo1(): 80
foo2(): 0
How is that difference explained?
Thank you for the previous answers and comments. They helped me understand the issue but I feel that none of them is completely clear, so here is an answer.
When I asked the question, I though that from config import global_variable would create a new binding (or "name") global_variable in the local package, but which would still bind to the same memory location as config.global_variable (two names for the same variable).
However, what seems to be true is that from config import global_variable creates a new variable global_variable in the local package, merely initialized by the value of config.global_variable. (To be more precise, for efficiency reasons global_variable probably still points to the same memory location as config.global_variable when it is created but, unlike a normal binding, it starts referring to some other memory location when assigned a new value).
For this reason, when I assign a new value to global_variable, I do not affect config.global_variable as originally expected, but instead change the value of the new variable global_variable.
So it seems that if I want a variable to be used across modules, I must always use the qualified form config.global_variable in all of them.