What does `return +/- ` do in python?

Question:

I was going through the CPython source code and I found the following piece of code from the standard library(ast.py).

if isinstance(node.op, UAdd):
   return + operand
else:
   return - operand

I tried the following in my python interpreter

>>> def s():
...     return + 1
...
>>> s()
1

But this is same as the following right?

def s():
    return 1

Can any one help me to understand what does the expression return + or return - do in python and when we should use this?

Asked By: user459872

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Source

Answers:

return + operand is equivalent to return operand (if operand is a number). The only purpose I see is to insist on the fact that we do not want the opposite of operand.

Answered By: Maxime Chéramy

Both + and - can be used as unary or binary operators. In your case they are used as unary operators. return + operand is the same as return operand. We are used to see them in the form of return +operand or return -operand.

Answered By: Sufian Latif

plus and minus in this context are unary operators. That is, they accept a single operand. This is in comparison to the binary operator * (for example) that operates on two operands. Evidently +1 is just 1. So the unary operator + in your return statement is redundant.

Answered By: OrenIshShalom

I haven’t studied the code, so I don’t know for sure, but Python allows overriding unary operator behavior:

__pos__(self) Implements behavior for unary positive (e.g. +some_object)

__neg__(self) Implements behavior for negation (e.g. -some_object)

So operand in your case could be an object of a class which overrides those magic methods.

This means that return + operand is NOT equivalent to return operand.

Answered By: warvariuc