carmellose carmellose - 3 months ago 7
Python Question

Best way to check function arguments in Python

I'm looking for an efficient way to check variables of a python function. For example, I'd like to check arguments type and value. Is there a module for this? Or should I use something like decorators, or any specific idiom?

def my_function(a, b, c):
"""an example function I'd like to check the arguments of."""
# check that a is an int
# check that 0 < b < 10
# check that c is not an empty string

Answer

The most Pythonic idiom is to clearly document what the function expects and then just try to use whatever gets passed to your function and either let exceptions propagate or just catch attribute errors and raise a TypeError instead. Type-checking should be avoided as much as possible as it goes against duck-typing. Value testing can be OK – depending on the context.

The only place where validation really makes sense is at system or subsystem entry point, such as web forms, command line arguments, etc. Everywhere else, as long as your functions are properly documented, it's the caller's responsibility to pass appropriate arguments.