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Python if x as y

I often find myself doing something stupid like

if some_function():
    self.value = some_function()

which makes the function execute twice. It will be fixed with something like

value = some_function():
if value:
    self.value = value

It would be great if Python allowed something like

if some_function() as value:
    self.value = value

Saves some space and is quite legible. I would even say it sounds pythonic.

So, I know this is invalid syntax, but is there a similar construct that I am not aware of? Should I be offering it to the Python Software Foundation?

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4 answers


Python intentionally disallows this construct by forcing the condition to if

be an expression and making the assignments not an expression, under the motto "Explicit is better than implicit". You have to write

value = some_function():
if value:
    self.value = value


(However, it works in Ruby, C, JavaScript, Java ... and any other language where assignment is an expression.)

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You can always do:



>>> self.value = some_function() or self.value
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def if_to_for(condition):
    if condition: yield condition

for value in if_to_for(some_function()):
    self.value = value

will work too.

If the condition is true, the loop will execute once, if it is false, it will not execute at all.

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theoretically :

if (lambda v: globals().update({'value':v}) or v)(some_function()):
    self.value = value

You are faster assigning the return of a function to a variable before you do if

. Also readability is calculated.

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