I have this code:
str = func(parameter)
if not str:
do something.
the function func() return a string on success and '' on failure.
The do something should happen only if str actualy contain a string.
Is it possible to do the assigmnt to str on the IF statment itself?
In one word: no. In Python assignment is a statement, not an expression.
Why not try it yourself,
if not (a = some_func()):
do something
^
SyntaxError: invalid syntax
So, no.
PEP 572 added syntax for assignment expressions. Specifically, using := (called the "walrus operator") for assignment is an expression, and thus can be used in if conditions.
if not (thing := findThing(name)):
thing = createThing(name, *otherArgs)
Note that := is easy to abuse. If the condition is anything more complex than a direct test (i.e. if value := expresion:) or a not applied to the assignment result (such as in the 1st sample above), it's likely more readable to write the assignment on a separate line.
With the below code snippet, if the func returns a string of length > 0 only then the do something part will happen
str = func(parameter)
if str:
do something
You can try this, it's the shortest version I could come up with:
if func(parameter):
do something.
func.