How can I fix "UnboundLocalError: local variable referenced before assignment"?

The following code gives the error UnboundLocalError: local variable 'Var1' referenced before assignment:

Var1 = 1
Var2 = 0
def function(): 
    if Var2 == 0 and Var1 > 0:
        print("Result 1")
    elif Var2 == 1 and Var1 > 0:
        print("Result 2")
    elif Var1 < 1:
        print("Result 3")
    Var1 -= 1
function()

How can I fix this?

You can fix this by passing parameters rather than relying on Globals

def function(Var1, Var2): 
    if Var2 == 0 and Var1 > 0:
        print("Result One")
    elif Var2 == 1 and Var1 > 0:
        print("Result Two")
    elif Var1 < 1:
        print("Result Three")
    return Var1 -= 1
function(1, 1)