Python enumerate for Looping with Counters

Presented by Philip from Real Python

Overview

• Introduction to the enumerate function in Python
• Using enumerate to simplify loops with counters
• Practical examples with a list of seasons: Spring, Summer, Fall, Winter
• Transition from basic loops to using enumerate

Topics Covered

1. Basic Looping

• Objective: Create a Python script to output the list of seasons with counters
• Task: Without using enumerate, produce the following output:
  • 1 Spring
  • 2 Summer
  • 3 Fall
  • 4 Winter

Example 1: Basic For Loop

• Define the seasons list: ['Spring', 'Summer', 'Fall', 'Winter']
• Use a basic for loop to iterate through the list and print each season

seasons = ['Spring', 'Summer', 'Fall', 'Winter']
for season in seasons:
    print(season)

• Output:
  • Spring
  • Summer
  • Fall
  • Winter

Example 2: Adding a Counter

• Introduce a count variable starting at 1
• Increment the count variable within the loop

count = 1
seasons = ['Spring', 'Summer', 'Fall', 'Winter']
for season in seasons:
    print(count, season)
    count += 1

• Output:
  • 1 Spring
  • 2 Summer
  • 3 Fall
  • 4 Winter

2. Using range and len

Example: Iterating with Indexes

• Use range and len to loop through seasons with indexes

seasons = ['Spring', 'Summer', 'Fall', 'Winter']
for i in range(len(seasons)):
    print(i + 1, seasons[i])

• Output:
  • 1 Spring
  • 2 Summer
  • 3 Fall
  • 4 Winter

Drawbacks of These Methods:

• count variable declared outside the loop
• Risk of incorrect placement of increment statement
• Harder to read and maintain code with range and len
• Limited to list (fails with sets)

3. Introducing enumerate

Example: Clean and Concise Loops

• Using enumerate to simplify the loop and count internally

seasons = ['Spring', 'Summer', 'Fall', 'Winter']
for count, season in enumerate(seasons, start=1):
    print(count, season)

• Output:
  • 1 Spring
  • 2 Summer
  • 3 Fall
  • 4 Winter

Advantages of enumerate:

• Clean and concise code
• Self-contained loop without external variable dependencies
• Avoids index management

4. Understanding enumerate

• Overview of what happens under the hood with enumerate
• Advantages of enumerating for loops revealed in the next lesson

Summary:

• enumerate offers a cleaner, more maintainable way of looping with counters
• Simplifies code by eliminating the need for external counter variables
• Makes for loops more readable and less error-prone