List Comprehension vs Dictionary Comprehension in Python and how to come up with dictionary comprehensions from 2 lists.

List Comprehension vs Dictionary Comprehension in Python

Python provides comprehensions as a concise way to create lists, dictionaries, and even sets. Two of the most common are list comprehension and dictionary comprehension. Let's explore their differences and how to use them — including combining two lists into a dictionary.

List Comprehension

A list comprehension creates a list by iterating over an iterable and applying an expression.

Syntax:

[expression for item in iterable if condition]

Example:

numbers = [1, 2, 3, 4, 5]
squares = [n**2 for n in numbers]
print(squares)  
# [1, 4, 9, 16, 25]

Here, squares is a list where each number is squared.

Dictionary Comprehension

A dictionary comprehension creates a dictionary with key–value pairs.

Syntax:

{key_expr: value_expr for item in iterable if condition}

Example:

numbers = [1, 2, 3, 4, 5]
square_dict = {n: n**2 for n in numbers}
print(square_dict)  
# {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

Here, each number is used as a key, and its square is the value.

Combining Two Lists into a Dictionary

Suppose you have two lists:

keys = ["a", "b", "c"]
values = [1, 2, 3]

You can combine them into a dictionary using dictionary comprehension.

1. Using zip()

The most Pythonic way:

my_dict = {k: v for k, v in zip(keys, values)}
print(my_dict)  
# {'a': 1, 'b': 2, 'c': 3}

zip() pairs elements from both lists until the shortest list ends.

2. Using Indexing with range()

If both lists are the same length:

my_dict = {keys[i]: values[i] for i in range(len(keys))}
print(my_dict)  
# {'a': 1, 'b': 2, 'c': 3}

3. Using enumerate()

By enumerating one list and indexing the other:

my_dict = {key: values[i] for i, key in enumerate(keys)}
print(my_dict)  
# {'a': 1, 'b': 2, 'c': 3}

4. Adding Conditions

You can filter while combining. For example, include only values greater than 1:

my_dict = {keys[i]: values[i] for i in range(len(keys)) if values[i] > 1}
print(my_dict)  
# {'b': 2, 'c': 3}

Basically, just keep these points in mind:

• List comprehension → creates a list.
• Dictionary comprehension → creates a dictionary (key–value pairs).
• You can combine two lists into a dictionary using:
  • zip() (most common)
  • range() with indexing
  • enumerate()
  • Filtering with conditions

If you have any questions, please let me know in the comment section, have a good day!