If the title is a bit cryptic (I have no idea how to put my issue in one title) here the explanation.
I have a global variable
ex = False
orig = id(ex)
Then, I have two functions:
def start(test):
print("Start")
global ex
while True:
if id(ex) == orig:
print("same")
else:
print(orig)
print(id(ex))
def end(test):
print("End")
global ex
ex = True
while True:
if id(ex) == orig:
print("same")
else:
print(orig)
print(id(ex))
When I enter the "end-function" the id of "ex" in the function is not the same as the original id. So, they are basically two different variables.
I do not understand why this happens. I mean, I know that it happens because I do set "ex = True" (because if I skip this line, the id is the same). But I do not understand why. I thought the idea of global keyword is exactly to make it possible to set global variables inside a function. Using global variables in a function
The problem is that bools are immutual. So when you change the global variable ex, you change to where it points to (i.e., a different object). You can easily simulate that:
>>> b=True
>>> id(b)
140715296352080
>>> b=False
>>> id(b)
140715296352112
>>> id(True)
140715296352080
>>> id(False)
140715296352112
If your variable would be of a mutual type and you change a value in it, it would not change the id. In the following example I place a wrapper around the bool
>>> class MyBool():
... val = False
...
>>> mb = MyBool()
>>> def foo():
... global mb
... print(id(mb))
... mb.val = True
... print(id(mb))
...
>>> foo()
2359703595472
2359703595472
And the id of the variable stays uncahnged.
In general, in python variables point to object in the global or local storage. When you change the "value" of a variable you need to distinguish between mutable and immutable types.