Assigning multiple values in an inline if/else statement

Question

I'm trying to write an inline if/else statement that assigns two values based on a single condition. Something to the effect of:

x = y = 0
value = 11
threshold = 5

x, y = x+1, 0 if value <= threshold else x, y = x-1, value

I'd expect this code to result in x = -1 and y = 11. When I run this, I get this error: SyntaxError: cannot assign to literal. I played around with parenthesis, but couldn't get anything to work.

Is there a way to do this? I can work around this, but this would be especially convenient.

Mark Tolonen · Accepted Answer · 2021-04-27 15:44:38Z

4

You need parentheses, and the extra x, y = after the else is not needed as well:

>>> x = y = 0
>>> value = 11
>>> threshold = 5
>>>
>>> x, y = (x+1, 0) if value <= threshold else (x-1, value)
>>> x
-1
>>> y
11

Note that without parentheses, you have a 3-tuple on the right side:

>>> x,y = x-1, value if value <= threshold else x+1, 0
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: too many values to unpack (expected 2)

It is parsed as: x+1, 0 if value <= threshold else x-1, value

edited Apr 27, 2021 at 15:44

answered Apr 27, 2021 at 4:54

Mark Tolonen

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1 Comment

Mark Tolonen Over a year ago

@LCVcode The typo is extraneous to the problem. I'll edit it out of both and we can delete these comments.

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