Force Python to return 0 when returning 0 or None

Question

I have a section in my code at the end of a recursive call that is as follows:

if (condition):
    # Some code here
else:
    return function_call(some_parameters) or function_call(some_parameters)

and it may evaluate to

return None or 0

where it will return 0 (an integer, as expected) or

return 0 or None

where it will return None (expected 0)

My question is, is it possible to have Python to return 0 (as an INTEGER) in the case immediately above?

Here is some code representing the scenario

$ cat test.py
#!/usr/bin/python3
def test_return():
    return 0 or None
def test_return2():
    return None or 0
def test_return3():
    return '0' or None #Equivalent of `return str(0) or None`

print( test_return() )
print( test_return2() )
print( test_return3() )

$ ./test.py
None
0
0

Note: 0 should be returned as an integer.

Why do you do that? Just type only 0, then it will return always 0. — Alperen, Sep 20 '17 at 06:22
... `x = fun(); y = f();` then `return x if x is not None else y` ? — juanpa.arrivillaga, Sep 20 '17 at 06:23
Check this question on StackOverflow: https://stackoverflow.com/questions/4477850/python-and-or-operators-return-value — Lame Fanello, Sep 20 '17 at 06:25
Similar one in https://www.quora.com/What-does-the-or-operator-mean-in-Pythons-return-statement — Monish K Nair, Sep 20 '17 at 06:32

score 3 · Answer 1 · answered Sep 20 '17 at 06:27

The Python behaves None, 0, {}, [], '' as Falsy. Other values will be considered as Truthy So the following are normal behavior

def test_return():
    return 0 or None   # 0 is Falsy so None will be returned
def test_return2():
    return None or 0   # None is Falsy so 0 will be returned
def test_return3():
    return '0' or None # '0' is Truthy so will return '0'

score 1 · Answer 2 · answered Sep 20 '17 at 06:36

You can use decorators, if its a specific case. Example below:

def test_return(f):
    def wrapper():
        result = f()
        if result == None or result == '0':
            return 0
        else:
            return result
    return wrapper

@test_return
def f1():
    return 0 or None

@test_return
def f2():
    return None or 0

@test_return
def f3():
    return '0' or None

Output:

print(f1())
print(f2())
print(f3())

0
0
0

Click here for further read on decorators.

score 0 · Answer 3 · answered Sep 20 '17 at 07:16

inline if else:

return 0 if (a == 0) + (b == 0) else None

by using the + arithmetic operator both a and b are evaluated, no 'shortcircuit' as with or

where a, b stand in for your function calls

tst = ((0, 0), (0, None), (None, 0), (None, None))


[0 if (a == 0) + (b == 0) else None for a, b in tst]
Out[112]: [0, 0, 0, None]

Force Python to return 0 when returning 0 or None

3 Answers3