Object type check

[king kikapu]

Hi to all,

in statically-types languages, let's say C# for example, we use
polymorphism through interfaces. So we define an interface I with
method M and then a class C that implements I interface and write code
for the M method.
So, if we have a function that takes a parameter of type I, we know
before-hand that it will have an M method to call.

But in dynamic languages this is not the case and we can pass whatever
we want to that function. Assuming that someone writes a library in
Python that other programmers will use, what is the correct way to
check inside that function if the parameter passed is of the correct
type, maybe "isinstance" BIF ?

Thanks in advance!