Using global variables between files?

Question

I'm bit confused about how the global variables work. I have a large project, with around 50 files, and I need to define global variables for all those files. What I did was define them in my projects `main.py` file, as following: ``` # ../myproject/main.py # Define global myList global myList myList = [] # Imports import subfile # Do something subfile.stuff() print(myList[0]) ``` I'm trying to use `myList` in `subfile.py`, as following ``` # ../myproject/subfile.py # Save "hey" into myList def stuff(): globals()["myList"].append("hey") ``` An other way I tried, but didn't work either ``` # ../myproject/main.py # Import globfile import globfile # Save myList into globfile globfile.myList = [] # Import subfile import subfile # Do something subfile.stuff() print(globfile.myList[0]) ``` And inside `subfile.py` I had this: ``` # ../myproject/subfile.py # Import globfile import globfile # Save "hey" into myList def stuff(): globfile.myList.append("hey") ``` But again, it didn't work. How s…

Accepted Answer

The problem is you defined `myList` from `main.py`, but `subfile.py` needs to use it. Here is a clean way to solve this problem: move all globals to a file, I call this file `settings.py`. This file is responsible for defining globals and initializing them:

```
# settings.py

def init():
    global myList
    myList = []
```

Next, your `subfile` can import globals:

```
# subfile.py

import settings

def stuff():
    settings.myList.append('hey')
```

Note that `subfile` does not call `init()`— that task belongs to `main.py`:

```
# main.py

import settings
import subfile

settings.init()          # Call only once
subfile.stuff()         # Do stuff with global var
print settings.myList[0] # Check the result
```

This way, you achieve your objective while avoid initializing global variables more than once.

Using global variables between files?

Solution

Problem