How to change a variable without making a new one in python

Question

Is it possible to change a variable without making a new one in python?

here is an example:

x = True


def reverseX():
  x = not x


print(x)
reverseX()
print(x)

now this will return an error because it thinks that I was making a new x in the reverseX thing is there a way for me to use the x that's at the top of the script in the reverseX thing?

btw, I know that I can use the return or just not use the reverseX thing, but sometimes you just need to use a def also, I know that I can pass the x variable through the call but is there another way?

Marko Borković · Accepted Answer · 2021-07-15T15:15:32.013

1

In your example you could do it by making x a global variable:

global x
x = True

def reverseX():
    global x
    x = not x

print(x)
reverseX()
print(x)

While this does work, I do not recommend it. As using global variables in more complex projects can lead to some problems, explained in this question. A much better way of doing it would be:

x = True

def reverseBool(var):
    return not var

print(x)
x = reverseBool(x)
print(x)

edited Jul 15 '21 at 15:15

answered Jul 15 '21 at 14:54

Marko Borković

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Thank you so much! I've been searching for this for too long – ZiyadCodes Jul 15 '21 at 15:03
2

And probably also explain [why `global` is basically always bad.](https://stackoverflow.com/questions/60439743/why-shouldnt-i-use-global-variables-in-python) – tripleee Jul 15 '21 at 15:10
@tripleee I edited the answer. Is it better now? – Marko Borković Jul 15 '21 at 15:16
Yup, much better. – tripleee Jul 15 '21 at 15:27
I really don't understand why you need the `global x` at the start of the script? When I remove it nothing happen. And when I keep it Pycharm gives me this warning: `Redeclared 'x' defined above without usage` – ZiyadCodes May 19 '22 at 17:30

How to change a variable without making a new one in python

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