Python, variable importing between files

Question

Preamble: I feel I probably have wasted so much time for a simple situation...

Now, I am making a game with pygame, and at some point, I wanted to split fil

Answer 1

TLDR: Use import configuration and fully qualified names, e.g. configuration.running.

If a function inside configuration needs to modify a top-level value, it must use global.

def decrease_HP(self):
    global running
    self.HP -= 1
    print("-1 HP", "Current HP:", self.HP)
    if self.HP <= 0:
        running = False

---

Using from configurations import running (or equivalent via ... import *) in main binds the value of configurations.running to a new name main.running. While these names initially share the same value, re-assigning either breaks this equivalency. This is exactly the same as rebinding other names.

>>> a = 1
>>> b = a  # a and b point to same value
>>> a == b
True
>>> b = 2  # rebind only b
>>> a == b
False

To make changes visible across the application, one should use an object an modify its value. A common example are containers, such as lists.

>>> a = [1]
>>> b = a  # a and b point to same value
>>> a == b
True
>>> b[0] = 2  # modify content of value of b
>>> a == b
True
>>> a[0] == b[0]  # content is the same
True

Since modules are objects, it is possible to use them directly to store state.

>>> import configuration
>>> b = configuration  # configuration and b point to same value
>>> configuration == b
True
>>> b.running = False  # modify content of value of b
>>> configuration == b
True
>>> configuration.running == b.running  # content is the same
True

---

Functions have local scope. Any assignment to a name inside a function implicitly declares the target as local to the function.

>>> running = True
>>> def stop():
...    running = False
...
>>> stop()  # changes only running inside the function
>>> running
True

This can be made visible by accessing a local name before it has a value.

>>> running = True
>>> def stop():
...    print(running)
...    running = False
...
>>> stop()
UnboundLocalError: local variable 'running' referenced before assignment

By declaring the name global, no local name is created. The global value can be directly read and written.

>>> running = True
>>> def stop():
...    global running
...    print(running)
...    running = False
...
>>> stop()  # will print the global value before the change
True
>>> running  # global value was changed
False