4

Is there a way to differentiate these two returned values?

>>> sort([1, 2, 3])
None

>>> dict(a=1).get('b')
None

The first returns None because there is no returned value. The second returns None as the returned value.

nathancahill
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3 Answers3

6

A function returning None, just returning or allowing execution to reach the end of the function is basically the same thing.

Consider the following functions:

def func1():
        return None

def func2():
        pass

def func3():
        return

If we now dissasemble the functions' bytecode (the dismodule can do that), we see the following

func1():
  2           0 LOAD_CONST               0 (None)
              3 RETURN_VALUE        
func2():
  5           0 LOAD_CONST               0 (None)
              3 RETURN_VALUE        
func3():
  8           0 LOAD_CONST               0 (None)
              3 RETURN_VALUE

The functions are identical. Thus there is no way you could distinguish between them, even by inspecting the functions themselves.

Krumelur
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1

No, there is not. The following functions all return the same value, None:

def a(): return None  # Explicitly return, explicitly with the value None
def b(): return       # Explicitly return, implicitly with the value None
def c(): pass         # Implicitly return, implicitly with the value None

You can't differentiate between the values returned by these functions because they all return the same thing.

Further reading: Python — return, return None, and no return at all

Community
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cdhowie
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1

If you're specifically asking about dict.get():

sentinel = object()
dict(a=1).get("b", sentinel)

Well written "lookup" APIs will either work that way (let you pass a custom 'not found' value) or raise some exception.

Else, well, no, None is None, period.

bruno desthuilliers
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