Scope

Where a name is visible

A name created inside a function exists only inside it:

def f():
    inside = 1     # local to f

f()
print(inside)      # NameError

Functions can read names from the surrounding module, but assigning to one creates a new local name rather than changing the outer one:

count = 0

def bump():
    count = count + 1     # UnboundLocalError

Python decides at compile time that count is local — because the function assigns to it — and then finds it has no value yet. The global keyword overrides that, but reaching for it is nearly always a sign the function should take an argument and return a result instead.

Mutating is different from assigning: a function can call .append() on an outer list, because that changes the object rather than rebinding the name.

Your turn: write bump(counter) that returns the counter plus one, without touching any global. Then use it to bring total to 3.