70 – Extract assignments from conditionals

Instead of using a conditional to make an assignment, use a conditional expression. This extracts the important operation (the assignment) out of the nesting of the if: ... else: ... statement, making it easier to spot the relevant part of the code.

If you’re not used to conditional expressions, it’s a matter of learning how to read them in English (or in your language). The snippet below, using a conditional statement, reads “If the user is logged in, set their permissions to "full", otherwise set them to "guest".”:

if logged_in:
    permissions = "full"
else:
    permissions = "guest"

If you use a conditional expression, it now reads as “Set the user permissions to "full" if the user is logged in, otherwise set them to "guest".”:

permissions = "full" if logged_in else "guest"
#^^^^^^^^^^^^^^^^^^^                           Set permissions to `"full"`
#                    ^^^^^^^^^^^^              if the user is logged in,
#                                 ^^^^^^^^^^^^ otherwise set them to `"guest"`.

Further reading:

• Conditional expressions.