How should I indent ternary conditional operator in python so that it complies with PEP8?

Question

PEP8 doesn't say anything about ternary operators, if I am not mistaken. So what do you suggest, how should I write long lines with ternary conditional operators?

some_variable = some_very_long_value \
                if very_long_condition_holds \
                else very_long_condition_doesnt_hold

or

some_variable = some_very_long_value \
                    if very_long_condition_holds \
                        else very_long_condition_doesnt_hold

Which one do you prefer the most?

Answer 1

Neither. For any long line, it's usually better to use parentheses to allow line breaks. Opinions differ whether you should do this:

some_variable = (some_very_long_value
                if very_long_condition_holds
                else very_long_condition_doesnt_hold)

or this:

some_variable = (
    some_very_long_value
    if very_long_condition_holds
    else very_long_condition_doesnt_hold)

or even this:

some_variable = (
    some_very_long_value
    if very_long_condition_holds
    else very_long_condition_doesnt_hold
)

Personally I prefer the third; Google in-house style is the second.

Answer 2

some_variable = (some_very_long_value
                 if very_long_condition_holds else
                 very_long_condition_doesnt_hold)

• Use parentheses instead of backslashes for line continuations, per PEP8.
• By putting the if ... else construct on its own line, there's a clear separation between the three parts of this expression: the then expression, the conditional part, and the else expression. The then and else expressions are formatted uniformly and are separate from the if...else construct.