How to Iterate Over Dictionary in Python: Complete Guide

Learning how to iterate over dictionary in Python is essential for working with key-value data structures. Python provides several methods to iterate through dictionaries, each serving different purposes. This guide covers all the techniques you need to effectively loop through dictionaries.

What is Dictionary Iteration? #

Dictionary iteration means accessing each element (key-value pair) in a dictionary sequentially. Unlike lists, dictionaries store data as key-value pairs, giving you multiple ways to access the data during iteration.

Basic Dictionary Setup #

Let's start with a sample dictionary that we'll use throughout this guide:

Method 1: Iterate Over Dictionary Keys #

The most basic way to iterate over dictionary in Python is to loop through the keys:

Key Points:

• Iterating directly over a dictionary gives you the keys
• Use dict.keys() to be explicit about iterating over keys
• Access values using dictionary[key] syntax

Method 2: Iterate Over Dictionary Values #

To iterate over only the values in a dictionary:

Use Cases:

• When you only need the values
• Calculating statistics (sum, average, max, min)
• Checking for specific values

Method 3: Iterate Over Dictionary Items (Key-Value Pairs) #

The most common and pythonic way to iterate over dictionary in Python:

Benefits:

• Most efficient for accessing both keys and values
• Clean, readable code
• Pythonic approach

Method 4: Iterate with Index (Enumerate) #

Sometimes you need both the position and the key-value pair:

Advanced Iteration Techniques #

Conditional Iteration #

Filter dictionary items during iteration:

Sorted Iteration #

Iterate in sorted order:

Dictionary Comprehension During Iteration #

Create new dictionaries while iterating:

Nested Dictionary Iteration #

When working with nested dictionaries:

Performance Considerations #

Dictionary Iteration Performance #

Different methods have different performance characteristics:

Performance Tips:

• Use items() when you need both key and value
• Use keys() only when you need just the keys
• Use values() only when you need just the values
• Avoid repeated dictionary lookups in loops

Common Patterns and Best Practices #

Pattern 1: Filtering and Transforming #

Pattern 2: Aggregation #

Error Handling During Iteration #

Handle potential errors when iterating over dictionaries:

Common Mistakes to Avoid #

1. Modifying Dictionary During Iteration #

2. Assuming Dictionary Order #

Summary #

When you need to iterate over dictionary in Python, remember these key techniques:

1. for key in dict: - Iterate over keys only
2. for value in dict.values(): - Iterate over values only
3. for key, value in dict.items(): - Iterate over key-value pairs (recommended)
4. enumerate(dict.items()) - Iterate with index
5. Conditional iteration - Filter during iteration
6. Sorted iteration - Process in sorted order

Best Practices:

• Use items() when you need both keys and values
• Use get() method for safe key access
• Don't modify dictionary during iteration
• Consider performance for large dictionaries
• Handle missing keys gracefully

Next Steps:

• Python Dictionary Complete Guide
• Dictionary Iteration Examples
• Advanced Dictionary Techniques