(Don\'t worry, this isn\'t another question about unpacking tuples.)
In python, a statement like foo = bar = baz = 5
assigns the variables foo, bar, and
https://docs.python.org/3/reference/simple_stmts.html#grammar-token-assignment_stmt
An assignment statement evaluates the expression list (remember that this can be a single expression or a comma-separated list, the latter yielding a tuple) and assigns the single resulting object to each of the target lists, from left to right.