Modules and Packages

• In the last series we had looked into modules & Packages

• We can also create sub packages.

• Then we can access the package and modules inside the packages using relative imports.

  • Look at this from .database import Database, the period(.) in front of database says use database module inside the current package
  • Look at his statement from ..database import Database we have two periods, navigate one level up (one folder/subpackage) an there we have a module called as database from that import class Database

• Now consider this statement from utilities.database.nosql.cassandra import Cassandra. Here are moving into sub packages.

Organize Content within module

• Inside any module, we can specify variables, classes, and/or functions
• We create some modules as libraries and some as executables.
• Refer the code from here
  • main.py is the module which we will be executing
  • This main.py uses number.py which acts as library.
• In some cases we might have the same module where we define methods/classes and executing the same module
• In this cases we need to organize the code in the module.
• If we don’t organize code our code might end up some thing like this

class Prime:
    def __init__(self, number):
        self.number = number

    def is_prime(self):
        pass


value = 11
prime = Prime(value)
if prime.is_prime():
    print("Prime number")
else:
    print("Not a prime")

• Every module has a special variable __name__ that specifies the name of the module when it was imported. But when the module is executed directly python prime.py, since there is no import that is happening __name__ variable will have a value __main__
• Using this logic prime.py can be changed to

class Prime:
    def __init__(self, number):
        self.number = number

    def is_prime(self):
        pass

def main():
    value = 11
    prime = Prime(value)
    if prime.is_prime():
        print("Prime number")
    else:
        print("Not a prime")



if __name__ == "__main__":
    # This module is executed directly 
    main()

    

• Refer test_prime.py file from here

• Next Steps:

  • Access Control in Classes
  • Third Party Libraries