I am trying to change number inside of function with change_value but as you can see it doesn't work
def change_value(number):
number += 1
def function():
number = 0
change_value(number)
print(number)
function()
When I run it, it prints out 0 instead of 1
In Python, all function parameters are passed by object sharing. This means you can mutate the value (if it is mutable), but you can never swap out a value for another (i.e. change the variable's binding, so that the original variable is affected).
Numbers are immutable. There is no way for you to do this.
If you place a number inside a mutable container (such as a list, a dict, or an object designed to do it), then you can do something like this:
def change_value(number_holder):
number_holder[0] += 1
def function():
number_holder = [0]
change_value(number_holder)
print(number_holder[0])
Objects of built-in types like (int, float, bool, str, tuple, unicode) are immutable in python. So, what you can do here is to return the modified variable and reassign it.
Code:
def change_value(number):
number += 1
return number
def function():
number = 0
number = change_value(number)
print(number)
function()
output:
1
Whereas, objects of built-in types like (list, set, dict) are mutable.
code:
def change_value(number):
number.append(1)
def function():
number = []
change_value(number)
print(number[0])
function()
output:
1
Here are some ways to achieve what you want
def change_value(number):
number[0] += 1
def function():
number = [0]
change_value(number)
print(number[0])
class myNumber:
def __init__(self, n):
self.num = n
def __add__(self, val):
self.num += val
def __repr__(self):
return str(self.num)
def change_value(number):
number += 1
def function():
number = myNumber(0)
change_value(number)
print(number)
I have changed two lines in your code to get your desired result:-
def change_value(number):
number += 1
return number # Returning an incremental value
def function():
number = 0
number = change_value(number)
print(number)
function()
Output
1
numberin yourchange_valuefunction is a different variable than the one in yourfunctionfunction.return numberinchange_valueand then you can donumber = change_value(number). This way everyone can see that you change value in variablenumber.