On 2/5/2021 2:51 AM, Paul Sokolovsky wrote:
((a, b) := (1, 2)) File "<stdin>", line 1 SyntaxError: cannot use assignment expressions with tuple
Why this accidental syntactic gap?
As should be clear from reading "Differences between assignment expressions and assignment statements", this 'gap' in entirely intentional, not accidental. *All* elaborations of 'name := expression' are listed and rejected as outside the scope of the proposal, which was to keep one reference to the expression value for later use. At least some of these elaborations were suggested and rejected during the voluminous discussion. The principal a.e. use in conditional expressions is testing for non-nullness. Your
while ((a1, b1) := phi([a0, a2], [b0, b2]))[0] < 5: a2 = a1 + 1 b2 = b1 + 1
is an unusual and very specific use. You want to have your tuple (for subscripting for testing) and eat it too (by unpacking). One can instead separate unpacking from testing a couple of ways while (tup := phi([a0, a2], [b0, b2]))[0] < 5: a2, b2 = tup a2 = a1 + 1 b2 = b1 + 1 while True: a1, b1 = phi([a0, a2], [b0, b2]) if a1 >= 5: break a2 = a1 + 1 b2 = b1 + 1 -- Terry Jan Reedy