Variable Tips

Understand local variables

Many things are confusing in Python, but few are as confusing as local and global variables. The scope of a local variable is restricted to the enclosing function but the scope of a global variable isn’t. What makes a variable local or global?

A variable is local in a function if it’s declared inside it, unless explicitly marked as global in the same function. Because the only way to declare a variable in Python is to use it on the left-hand side (LHS) of an assignment statement, Python variables are always initialized. Whether or not a variable in a function is global, doesn’t depend on whether a global variable with the same identifier already exists. If it does, the function may have a local variable with the same name that will shadow the global variable, making it invisible in the function.

Let gv = 1 be a global variable. The variable remains global in the following two functions.

• f1() treats gv as a global because it is marked as global, despite the assignment statement.

• f2() treats gv as a global because there is no assignment statement.

Let’s try the code below.