1. import math_operations
   1. math_operations.add()
2. from math_operations import add,subtract
   1. result = add(2,3)
3. from math_operations import add as addition
   1. result = addition(4,6)
4. the name variable contains the name of the current module
   1. when we run this math_o.py drectly, the code inside the if name == main block will be executed,
   2. however we import ‘math_operations.py’ into ‘main.py’, the code inside the if name == main will not executed
5. from my_package import module1 as m1
6. from mypackage import *
7. external pip
   1. pip install -r requirements.txt