python 0 assigner returns none despite the value

Question

I have a problem in python(python 3.9 on VS Code). I'm trying to change a value in a dictionary by some conditions:

def getset(age):
    age['age']+=0 if age['age']>=0 else age['age'] == 0
mammad = {'name': 'mammad', 'age': -3}
mammad = getset(mammad)
print(mammad)

as you can see in age['age']+=0 if age['age']>=0 else age['age'] == 0 age key has to have a value of 0 if it's lower than 0. But anyway, it changes it to none. What's the problem?

Answer 1

You need to return the dict after you make changes to it (you are assigning None from the function call when it returns nothing) or just call the function without assigning it to your variable since it will modify the dict in-place anyway. You can change the dictionary like this:

def getset(age):
    age['age'] = 0 if age['age'] < 0 else age['age']

mammad = {'name': 'mammad', 'age': -3}
# no need to 'assign' to 'mammad' again, you changed it already!
getset(mammad)
>>> print(mammad)
{'name': 'mammad', 'age': 0}

A function which returns nothing prints nothing (None).

>>> def f():
...     pass
... 
>>> print(f())
None