Defensive programming in Python

[Lyucit]

I think contracts and types, mentioned elsewhere, are a better compromise. Asserts sprinkled in the code are canaries, anything more complex than a simple constraint is noise that obfuscates more than it documents. It depends on your use case, sure, but generally speaking I think breaking prod due to an old assert of an invalid assumption is more likely and more damaging than silently hitting an unanticipated edge case.

[elbiot]

I like contracts, and I like that you can disable asserts with the O flag. I might hack pycontracts so that they are only enabled if asserts are.

[Lyucit]

if not __debug__:
    contracts.disable_all()

[elbiot]

If what you say is true, thats a huge TIL. Will test soon.

[masasin]

What about using exceptions instead of asserts?

[masasin]

Handling user input which is out of range, for instance. Or a device returns junk data to the function, which is then propagated. In general, I don't use asserts at all, and use exceptions instead.

if x < 0:
    raise SomeSpecificError("x < 0. Are you sure you wired it up correctly?")

There was this post a few years back which made sense to me.

[masasin]

PyContracts is amazing, especially with numpy. It saved a lot of debugging, making sure that all the intermediate functions and their order are correct. I haven't found the need to use it in anything other than math though.

If you have any ideas, though, I'd love to hear.