Comment by sdfgioafnui

Exceptions are for exceptional circumstances. An object being a certain type is not an exceptional circumstance, not even in a dynamic language. You should never be surprised by the type of an object unless your program has serious design flaws.

The fact that the language doesn't have your back means you need to be more careful about types, not less. The type of the arguments is a function precondition. It's the callee's responsibility to document preconditions and ideally recover cleanly from a violation, but the caller's responsibility to ensure preconditions are met. Illegal states should be caught early, not allowed to percolate until an exception is thrown.

I don't much care if what I just wrote is "Pythonic" or not. I don't think too much careful design up front is responsible for every Python codebase I've ever seen reading like Finnegan's Wake.