How to write Python if else in single line?

Question

category.is_parent = True if self.request.get('parentKey') is not None else category.is_parent = False

Above is the code in which I am trying to write a if else in a single line and it is giving me this syntax error

SyntaxError: can't assign to conditional expression"

But if I write it in following way it works fine

if self.request.get('parentKey') is not None: category.is_parent = True else: category.is_parent = False

You don't need an id/else here. Just do category.is_parent = self.request.get('parentKey') != None — lovasoa
– lovasoa, Commented Nov 25, 2016 at 17:44
If you put it on one line, it's a slightly different syntax. x = a if condition else b, and you can chain multiple ones up too, like x = a if condition else b if condition2 else c — Peter
– Peter, Commented Nov 25, 2016 at 17:44
The structure you tried is '<assignment> if condition else <assignment>'; the structure that's allowed is 'variable = <expression>' where expression is of the form '<value1> if <condition> else <value2>'. — Jonathan Leffler
– Jonathan Leffler, Commented Nov 25, 2016 at 17:46

ettanany · Accepted Answer · 2016-11-25 19:37:16Z

3

Try this:

category.is_parent = True if self.request.get('parentKey') else False

To check only against None:

category.is_parent = True if self.request.get('parentKey') is not None else False

edited Nov 25, 2016 at 19:37

answered Nov 25, 2016 at 17:41

ettanany

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4 Comments

Moses Koledoye Over a year ago

This isn't exactly the same with what the OP wants. Doesn't handle the case where self.request.get('parentKey') is falsy and not None

ettanany Over a year ago

@SaimAbdullahCh You can accept it as the answer of your question :)

ettanany Over a year ago

@MosesKoledoye How do you know that?

Moses Koledoye Over a year ago

Because '', 0, [] etc. will all return False, but it should be True in this case.

Artem Yu · Accepted Answer · 2016-11-25 17:44:02Z

You can write:

category.is_parent = True if self.request.get('parentKey') is not None else False

Or even simpler in this case:

category.is_parent = self.request.get('parentKey') is not None

Kofi Nartey · Accepted Answer · 2022-11-28 18:29:49Z

You can write this with a one liner but using the [][] python conditional syntax. Like so:

category.is_parent = [False,True][self.request.get('parentKey') is not None

The first element in the first array is the result for the else part of the condition and the second element is the result when the condition in the second array evaluates to True.

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