Class invariants in Python

Question

Class invariants definitely can be useful in coding, as they can give instant feedback when clear programming error has been detected and also they improve code readability as b

Answer 1

Please have a look at icontract library. We developed it to bring design-by-contract into Python with informative error messages. Here as an example of a class invariant:

>>> @icontract.inv(lambda self: self.x > 0)
... class SomeClass:
...     def __init__(self) -> None:
...         self.x = 100
...
...     def some_method(self) -> None:
...         self.x = -1
...
...     def __repr__(self) -> str:
...         return "some instance"
...
>>> some_instance = SomeClass()
>>> some_instance.some_method()
Traceback (most recent call last):
 ...
icontract.ViolationError: self.x > 0:
self was some instance
self.x was -1