4 ms·

I don't think so. The assignment behavior here is explicit, not some emergent fact of operator chaining in general. I think it's meant to allow you to say a

I don't think so. The assignment behavior here is explicit, not some emergent fact of operator chaining in general. I think it's meant to allow you to say a = b = expr and have both a and b end up with the value of expr. And by defining it in the fashion that it does, it only requires the target list expressions to be evaluated once as an lvalue (or whatever python's equivalent is).

lilyball 5y ago
Thinking about it some more, the surprising behavior here is pretty much just that it does the assignments in left-to-right order instead of right-to-left order. If you try and break down `a = b = expr` into a series of binary assignment operators, the natural answer is `a = (b = expr)` (b doesn't exist yet so you can't write `(a = b) = expr`) where `(b = expr)` behaves as though it returns the value again. And I believe this is in fact how it works in Ruby (as Ruby assignments return the value). But Python assignments don't actually return the value, as they are statements and not expressions. Presumably Python does the assignments in left-to-right order because any observable side-effects in the evaluations of a and b would be expected to be in left-to-right order. It just results in counterintuitive behavior like this.