What Are Modules?

• Think of a module as a code library, a file that contains a set of functions and variables that you want to include in your application.

Built-in Modules:

• Python has several built-in modules that you can import and use whenever you like.

Example: Importing a Built-in Module:

• Import and use the platform module:

  python

  import platform
  
  x = platform.system()
  print(x)  # Output might be: 'Windows', 'Linux', or 'Darwin' (for Mac)
  

Using the dir() Function:

• The dir() function lists all the function names (or variable names) in a module.

Example: Listing Names in a Module:

import platform

x = dir(platform)
print(x)  # Output: A list of all the defined names in the platform module

Importing Specific Parts from a Module:

• You can choose to import only specific parts of a module using the from keyword.

Example: Importing Specific Parts:

• Consider a module named mymodule with a function and a dictionary:

  python

  def greeting(name):
      print("Hello, " + name)
  
  person1 = {
      "name": "John",
      "age": 36,
      "country": "Norway"
  }
  

• Importing only the person1 dictionary from mymodule:

  python

  from mymodule import person1
  
  print(person1["age"])  # Output: 36
  

  • Note: When importing using the from keyword, refer to the elements directly, not using the module name (e.g., person1["age"] instead of mymodule.person1["age"]).

Exercises:

1. Import and Use a Built-in Module:

   • Import the math module and print the square root of 25.

     python

     import math
     
     print(math.sqrt(25))  # Output: 5.0
     

2. List Names in a Module:

   • Use the dir() function to list all names in the random module.

     python

     import random
     
     print(dir(random))  # Output: A list of all defined names in the random module
     

3. Import Specific Parts:

   • Create your own module with a function and a variable. Import only the variable and use it in your code.

     python

     # mymodule.py
     def greet(name):
         print("Hi, " + name)
     
     age = 15
     
     # main.py
     from mymodule import age
     
     print(age)  # Output: 15
     

Summary:

• Modules help organize and reuse code in Python. They can be built-in or user-defined. Practice importing and using modules to understand how to leverage these useful libraries in your programs!