What is this kind of assignment in Python called? a = b = True

Question

I know about tuple unpacking but what is this assignment called where you have multiple equals signs on a single line? a la a = b = True

It always trips me up a bit especially when the RHS is mutable, but I'm having real trouble finding the right keywords to search for in the docs.

Answer 1

It's a chain of assignments and the term used to describe it is...

^{- Could I get a drumroll please?}

Chained Assignment.

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I just gave it a quite google run and found that there isn't that much to read on the topic, probably since most people find it very straight-forward to use (and only the true geeks would like to know more about the topic).

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In the previous expression the order of evaluation can be viewed as starting at the right-most = and then working towards the left, which would be equivalent of writing:

b = True
a = b

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The above order is what most language describe an assignment-chain, but python does it differently. In python the expression is evaluated as this below equivalent, though it won't result in any other result than what is previously described.

temporary_expr_result = True

a = temporary_expr_result
b = temporary_expr_result

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Further reading available here on stackoverflow:

• How do chained assignments work? python