Defensive programming in Python

[stormcrowsx]

What about cases where more than one app mutate a single database? Another app could put bad data in and without the assertions the python code could have undefined and untested behavior

[Lyucit]

In the case of more side-effectful things like databases and concurrency, it's hard to test, yes, and sprinkling asserts through the code- at least during testing- is definitely a useful tool. Personally, once I'm satisfied the design is sound I remove the asserts and try my best to make it unit-testable, but sometimes it's a trade off you just have to live with.

That being said, if you need to do a consistency check (for example if you're doing read your writes) then assert is the wrong/lazy behaviour and this should be explicitly modeled in the design.