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

Answer 1

got bitten by python's Chained Assignment today, due to my ignorance. in code

if l1.val <= l2.val:
    tail = tail.next = l1 # this line 
    l1 = l1.next

what I expected was

tail.next = l1
tail = tail.next
# or equivalently 
# tail = l1

whereas I got below, which produce a self loop in the list, leave me in a endless loop, whoops...

tail = l1
tail.next = l1 # now l1.next is changed to l1 itself

since for a = b = c, one way (python, for example) equivalent to

tmp = evaluate(c)
evaluate(a) = tmp
evaluate(b) = tmp

and have equal right operand for two assignment.

the other (C++, for example) equivalent to

evaluate(b) = evaluate(c)
evaluate(a) = evaluate(b)

since in this case a = b = c is basically

b = c
a = b

and two right hand operand could be different.

That why similar code works well in C++.