Introduction to Classes in Python

Overview

• Learn about creating and using classes in Python.
• Topics will cover:
  • Basics of creating/instantiating classes
  • Inheritance
  • Class and instance variables
  • Static and class methods
  • Other advanced topics

Why Use Classes?

• Allow logical grouping of data (attributes) and functions (methods).
• Reusable and easy to build upon.

Terms to Know

• Attributes: Data associated with a class.
• Methods: Functions associated with a class.

Creating a Simple Class

Blueprint for Instances

• Example application: Represent employees in Python code.
• Each employee can have specific attributes (e.g., name, email, pay) and methods (actions).
• Define a class:

  class Employee:
      pass
  

Instantiating Classes

• Instance: A unique object created using the class blueprint.

  employee_1 = Employee()
  employee_2 = Employee()
  

• Each instance is a unique object in memory.

Instance Variables

• Contain data unique to each instance.
• Set manually:

  employee_1.first_name = "Corey"
  employee_1.last_name = "Schaefer"
  employee_1.email = "[email protected]"
  employee_1.pay = 50000
  

• Manually setting many attributes for each instance is cumbersome and error-prone.

Using the __init__ Method

Purpose

• Initialize instance variables when the instance is created.
• Acts like a constructor from other programming languages.

Example

• Define __init__ method:

  class Employee:
      def __init__(self, first, last, pay):
          self.first = first
          self.last = last
          self.pay = pay
          self.email = f"{first}.{last}@company.com"
  

• Automatically called when an instance is created:

  employee_1 = Employee("Corey", "Schaefer", 50000)
  employee_2 = Employee("Test", "User", 60000)
  

Creating Methods

Example: Full Name Method

• Define a method within the class:

  class Employee:
      def __init__(self, first, last, pay):
          self.first = first
          self.last = last
          self.pay = pay
          self.email = f"{first}.{last}@company.com"
  
      def full_name(self):
          return f"{self.first} {self.last}"
  

• Use method with an instance:

  print(employee_1.full_name())  # Output: Corey Schaefer
  print(employee_2.full_name())  # Output: Test User
  ``
  

Calling Method via Class

• Alternative way to call method using class name:

  print(Employee.full_name(employee_1))  # Output: Corey Schaefer
  

• Must pass instance manually.

Common Mistake: Forgetting self

• Omitting self in method definitions can lead to errors:

  class Employee:
      def full_name():  # Missing `self`
          return f"{self.first} {self.last}"
  

• Always include self as the first argument in method definitions.

Conclusion

• Basics of creating classes and instances.
• Initializing attributes using __init__.
• Creating and using methods.

Next Steps

• Future videos will cover class variables and more advanced topics.

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