How to identify number of atoms in a structure using pymatgen?

Materials Project Materials Project Data/API
1

How to identify number of atoms in a structure using pymatgen? What is the property name?

2

Since the Structure object is implemented as an iterable sequence of Site objects, I expect you can just use len(list(my_structure)) to find the number of atoms in my_structure.

3

The attribute is called num_sites

4

I used this @Nicholas_Winner but I got None