what are the header files in python?

Answer 1

You can import header file by using keyword 'import'.
Ex: import os
import sys
import datetime
import smtp

Answer 2

but what are os ,sys,datetime,and smtp?

Answer 3

Header files can be imported to your code to extend your capabilities to use other functions and classes.

It is trivial to import math header for example if you don't have own code to calculate square root of numbers when needed.