Function xyz returns two values a and b:
def xyz(): return a, b
Code calling xyz stores result into one variable assuming xyz returns only one value:
t = xyz()
t is actually a tuple (a, b) so any action on
t assuming it is not a tuple may fail deep in the code with a an unexpected error about tuples.
TypeError: type tuple doesn't define ... method
The fix would be to do:
a, b = xyz()
Beginners will have trouble finding the reason of this message by only reading the tuple error message !