What does the python operator =- do?

Question

What does the python operator =- do? I'm not asking about the -= operator, which I realize is shorthand for x = x - value.

Have you tested it? Break it down, don't think about it as 1 operator but two: = and -. Thus x =- x is negating x as a number. — Andrew Li
– Andrew Li, Commented May 26, 2017 at 13:25
@Roberto What do you mean "not valid python syntax"? It's completely valid. — Andrew Li
– Andrew Li, Commented May 26, 2017 at 13:26

timgeb · Accepted Answer · 2017-05-26 13:29:54Z

7

Actually, the operator =- does not exist. It is only = (- value). So the negative of the value.

Example:

>>> x =- 1
>>> x
-1

edited May 26, 2017 at 13:29

timgeb

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answered May 26, 2017 at 13:25

Divisadero

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1 Comment

timgeb Over a year ago

Yep, x =- 1 just looks weird.

user33484 · Accepted Answer · 2017-05-26 13:26:51Z

2

Why not test it?

In [11]: x = 1

In [12]: y = 2

In [13]: y=-x

In [14]: y
Out[14]: -1

As you can see it does nothing, but sets a negative value of the variable on the right hand side

answered May 26, 2017 at 13:26

user33484

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Comments

freakish · Accepted Answer · 2017-05-26 13:45:03Z

1

There is no =- operator. Depending on the context this might be two operators, e.g. x =- y is equivalent to x = (-y) (so there are two operators: assignment and negation) or an assignment with a negative constant: x =- 1 is equivalent to x = (-1) (in this context - is not an operator, it's just a negative constant).

edited May 26, 2017 at 13:45

answered May 26, 2017 at 13:29

freakish

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1 Comment

freakish Over a year ago

@timgeb github.com/python/cpython/blob/… As you can see - is parsed directly, there is no __neq__ call in case of constants.

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