Python How to Convert Two Lists to Dictionary Easily

You can convert two lists to a dictionary in Python by using dict(zip(list1, list2)), which pairs elements from both lists as key-value pairs.

Examples

Inputlist1 = ['a', 'b'], list2 = [1, 2]

Output{'a': 1, 'b': 2}

Inputlist1 = ['name', 'age'], list2 = ['Alice', 30]

Output{'name': 'Alice', 'age': 30}

Inputlist1 = [], list2 = []

Output{}

How to Think About It

To convert two lists into a dictionary, think of matching each item in the first list as a key with the corresponding item in the second list as its value. You pair them one by one and then create a dictionary from these pairs.

Algorithm

1

Take the first list as keys.

2

Take the second list as values.

3

Pair each key with its corresponding value.

4

Create a dictionary from these pairs.

5

Return the dictionary.

Code

python

list1 = ['a', 'b', 'c']
list2 = [1, 2, 3]
dictionary = dict(zip(list1, list2))
print(dictionary)

Output

{'a': 1, 'b': 2, 'c': 3}

Dry Run

Let's trace converting list1 = ['a', 'b', 'c'] and list2 = [1, 2, 3] into a dictionary.

1

Pair elements

Pairs formed: ('a', 1), ('b', 2), ('c', 3)

2

Create dictionary

Dictionary created: {'a': 1, 'b': 2, 'c': 3}

Key	Value
'a'	1
'b'	2
'c'	3

Why This Works

Step 1: Using zip

The zip function pairs elements from two lists by their positions, creating pairs like (key, value).

Step 2: Creating dictionary

The dict function takes these pairs and makes a dictionary where the first item is the key and the second is the value.

Alternative Approaches

Using dictionary comprehension

python

list1 = ['a', 'b', 'c']
list2 = [1, 2, 3]
dictionary = {list1[i]: list2[i] for i in range(len(list1))}
print(dictionary)

This method is clear and flexible but requires both lists to be the same length.

Using a loop

python

list1 = ['a', 'b', 'c']
list2 = [1, 2, 3]
dictionary = {}
for i in range(len(list1)):
    dictionary[list1[i]] = list2[i]
print(dictionary)

This is more verbose but easy to understand for beginners.

Complexity: O(n) time, O(n) space

Time Complexity

The process loops through both lists once to pair elements, so it takes linear time proportional to the list size.

Space Complexity

A new dictionary is created with as many entries as the length of the lists, so space grows linearly.

Which Approach is Fastest?

Using dict(zip()) is the fastest and most readable; dictionary comprehension and loops are slightly slower but offer more control.

Approach	Time	Space	Best For
dict(zip())	O(n)	O(n)	Simple and fast conversion
Dictionary comprehension	O(n)	O(n)	When you want more control or conditions
Loop with assignment	O(n)	O(n)	Beginners learning step-by-step