I don't know why the functions is not using the if when the code works outside the function

Question

word = input() #"3 is crowd"

nonum = ""

def change(a):
print(a)
if str(a) in word:
nonum = word.replace(str(a),"three")

change(3)
print(nonum)

# this returns 3
#-----------------------------------------
word = input() #"3 is crowd"

nonum = ""

if str(3) in word:
nonum = word.replace(str(3),"three")

print(nonum) #this prints "three is crowd" which is the desired outcome

#the only difference is if the if is inside the change() function
#why is the if function not working when called inside change()?

Answer 1

There's no problem with the function, and the `if` conditional.

The problem is, the <nonum> inside the function is local, it's not the same with the <nonum> defined outside the function - at global space.

If you want to change a global variable in a function you need to specify that explicitly by adding

global nonum

One line above the replacement of 3 -> "three" statement, inside the `if` block