When should I use type checking (if ever) in Python?

Question

I'm starting to learn Python and as a primarily Java developer the biggest issue I am having is understanding when and when not to use type checking. Most people seem to be saying that Python code shouldn't need type checking, but there are many cases when I believe it is necessary. For example, let's say I need to use a method parameter to perform an arithmetic operation, why shouldn't I make sure the argument is a numeric data type?

This issue is not only limited to functions. The same thought process occurs to me for class variables. Why and when should I or shouldn't I use properties (using @property) to check type instead of regularly implemented class variables?

This is a new way of approaching development for me so I would appreciate help understanding.

Answer 1

It's not Pythonic to check type info, use duck typing instead: if it looks like a duck, walks like a duck and quacks like a duck then it is a duck.

def quack(duck):
    duck.quack()

this will only run if duck has a callable quack attrubute, it will raise an exception otherwise which can be caught by the caller.