>>> x = 5
>>> y = 3
>>> assert x < y, "x has to be smaller than y"
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AssertionError: x has to be smaller than y
>>>
assert should not be used to catch programming errors like
x / 0, because Python traps such programming errors itself!
assert is for trapping user-defined constraints!