The most common reason for this error is that you’re using multiple global declarations in the same function. Consider this example:

x = 0

def func(a, b, c):
if a == b:
global x
x = 10
elif b == c:
global x
x = 20

If you run this in a recent version of Python, the compiler will issue a SyntaxWarning pointing to the beginning of the func function.

Here’s the right way to write this:

x = 0

def func(a, b, c):
global x # <- here
if a == b:
x = 10
elif b == c:
x = 20