UnboundLocalError

Qué causa este error

You read a variable before assigning to it within the same function. Python sees the assignment and treats the variable as local for the entire function, so reading it before the assignment fails. This often happens when trying to modify a global variable without the global keyword.

Cómo solucionarlo

Use the global keyword to reference global variables: global x. Or use nonlocal for enclosing scope variables. Restructure code to assign the variable before reading it. Pass the value as a function parameter instead.

x = 10
def f(): print(x); x = 20
f()  # UnboundLocalError