pfctdayelise pfctdayelise - 11 months ago 57
Python Question

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

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.


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

- Could I get a drumroll please?

Chained Assignment.

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).

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

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

Further reading available here on stackoverflow: