Python Variables

Variables in Python

Introduction

• Using variables in Python enhances its capabilities beyond being a simple calculator.

• Variables offer numerous advantages over using raw numbers directly.

Creating Variables

• Creating a variable in Python is straightforward.

• Example: python mv_population = 74728

  • mv_population is the variable name.

  • The = sign is the assignment operator.

  • 74728 is the value assigned to the variable.

• The assignment operator assigns the value on the right to the variable on the left.

• The left side becomes a name for the value on the right side.

Variable Usage

• Example: python x = 2 y = x print(y)

  • x is defined as 2.

  • y is defined as the value of x (which is 2).

  • The value of y is accessed using its name.

Variable Definition

• Accessing an undefined variable results in an error.

• Error message example: NameError: name 'z' is not defined.

Multiple Assignments

• Python allows assigning multiple variables simultaneously.
  python x = 2 y = 3 z = 5

• Can be abbreviated as:
  python x, y, z = 2, 3, 5

• Useful for assigning related variables like width, height, or coordinates.

Variable Naming

• Descriptive variable names enhance code clarity.

• Example:
  python population_density = mountain_view_population / mountain_view_land_area

Naming Conventions and Restrictions

• Allowed characters: letters, numbers, and underscores.

• Cannot contain spaces.

• Must start with a letter or underscore.

• Avoid reserved words or built-in identifiers.

• Using a reserved word as a variable name can cause errors or conflicts.

• Pythonic naming convention: use lowercase letters and underscores to separate words.

Updating Variables

• Variables can be updated by reassigning them.

• Example:
  python mv_population = 78128

• Updating based on changes:
  python mv_population = mv_population + 4000 - 600

• In this line, the variable mv_population is being assigned to itself plus $4,000$ minus $600$, resulting in $78,128$.

Assignment Operators

• Special assignment operators simplify increment and reassign operations.

• Example:
  python mv_population += 4000 # Incrementing mv_population by 4000

• += operator increments the variable on the left by the value on the right.

• Other assignment operators: -=, *=, /=, etc.

• These operators apply the arithmetic operation to the variable on the left with the value on the right.

• Using assignment operators makes the code concise.