How does Python process a statement with both assignment and a comparison?

Question

I've got the following line:

group_index = apps["special_groups"] == group

From my understanding, group_index is being assigned the value in apps["special_groups"]. Then I see the == operator, but what does it do with the result? Or is it comparing apps["special_groups"] to group first?

Barmar · Accepted Answer · 2015-09-09 20:14:31Z

4

From the Python Evaluation Order documentation:

Notice that while evaluating an assignment, the right-hand side is evaluated before the left-hand side.

So it first evaluates apps["special_groups"] == group, then assigns the result of this to group_index.

answered Sep 9, 2015 at 20:14

Barmar

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1 Comment

dpdwilson Over a year ago

Beat me by less than a minute! Shouldn't have stopped for that sip of water :P

dpdwilson · Accepted Answer · 2015-09-09 20:16:04Z

1

From the Python docs, Section 5.14:

Python evaluates expressions from left to right. Notice that while evaluating an assignment, the right-hand side is evaluated before the left-hand side.

Therefore it evaluates the right-hand side, apps["special_groups"] == group, first, and then it assigns this result to the left-hand side, group_index.

answered Sep 9, 2015 at 20:16

dpdwilson

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Comments

mpcabd · Accepted Answer · 2015-09-09 20:11:37Z

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It assigns the value of the boolean comparison [True or False] to the LHS variable group_index.

answered Sep 9, 2015 at 20:11

mpcabd

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