Question

I read PEP 8: Style Guide for Python and I wasn’t quite sure how to style mathematical operators inside arguments.

For example, for the = sign PEP 8 says

Yes:
    x = 3
    y = foo(bar=3)
No:
    x=3
    y = foo(bar = 3)

But what about other mathematical operators like -, +, /, etc. Which is good style?

foo_bar = bar[i - 3][j + 2]
z = foobar(y=i - 1, z=k + 2)

or

foo_bar = bar[i-3][j+1]
z = foobar(y=i-1, z=k+2)

?

To be honest, the latter looks better in my opinion.

From PEP 8:

Other Recommendations

• Always surround these binary operators with a single space on either side: assignment (=), augmented assignment (+=, -= etc.), comparisons (==, <, >, !=, <>, <=, >=, in, not in, is, is not), Booleans (and, or, not).

• Use spaces around arithmetic operators:

• Don’t use spaces around the = sign when used to indicate a keyword argument or a default parameter value.

Answer 1

Right up at the top of Pep 8 is this advice:

But most importantly: know when to be inconsistent — sometimes the style guide just doesn’t apply. When in doubt, use your best judgment.

There are two exceptions made explicit, and I think argument passing falls under this:

1. When applying the rule would make the code less readable, even for someone who is used to reading code that follows the rules.

I’d leave out the spaces in the arguments, making your example:

foo_bar = bar[i - 3][j + 2]
z = foobar(y=i-1, z=k+2)