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.