How do I create or use a global variable inside a function?
How do I use a global variable that was defined in one function inside other functions?
Failing to use the global keyword where appropriate often causes UnboundLocalError. The precise rules for this are explained at UnboundLocalError on local variable when reassigned after first use. Generally, please close other questions as a duplicate of that question when an explanation is sought, and this question when someone simply needs to know the global keyword.