Question

e.g. D, if sum_p is not zero.

D = 1/sum_p if sum_p \
    else 0

What if I want to return the value? Should I do:

return 1/sum_p if sum_p \
else 0

or just write

if...
else: return 0

Answer 1

If you want to do a single statement conditional return, use:

return 1 / sum_p if sum_p else 0

This is not an if statement. It’s a conditional expression. Think of it as

return (this_value if this_condition_is_true else that_value)

The return itself is outside the conditional.

If the line is long enough you have to split it up, stylistically I’d recommend using an ordinary if statement and two return statements.

In general, don’t use \ as a line terminator. PEP-8 recommends you always use parenthesis:

The preferred way of wrapping long lines is by using Python’s implied line continuation inside parentheses, brackets and braces. Long lines can be broken over multiple lines by wrapping expressions in parentheses. These should be used in preference to using a backslash for line continuation. Make sure to indent the continued line appropriately. The preferred place to break around a binary operator is after the operator, not before it. Some examples: