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Python Program to Create a Dictionary from Two Lists

Beginner · Dictionaries

Two lists often belong together, like a list of names and a list of their marks. This program pairs the first item of one list with the first item of the other, and so on, and stores the pairs in a dictionary with the first list as the keys.

Program

dictionary_from_two_lists.py
names = ["Riya", "Arjun", "Meera", "Kabir"]
marks = [88, 72, 95, 64]
result = {}
for i in range(len(names)):
result[names[i]] = marks[i] # the name is the key, the mark is the value
print("Keys: ", names)
print("Values:", marks)
print("Dictionary:", result)
print("Meera scored", result["Meera"])
Output
Keys:   ['Riya', 'Arjun', 'Meera', 'Kabir']
Values: [88, 72, 95, 64]
Dictionary: {'Riya': 88, 'Arjun': 72, 'Meera': 95, 'Kabir': 64}
Meera scored 95

How it works

  1. The loop runs once for each position i in the list of names.
  2. result[names[i]] = marks[i] adds an entry whose key is the name at that position and whose value is the mark at the same position.
  3. Once the dictionary is built, a mark can be looked up by name, like result["Meera"], instead of by position.
  4. Keys are unique, so if a name appeared twice in names, the later mark would replace the earlier one.
  5. The loop expects the lists to be the same length; if marks were shorter, marks[i] would raise an IndexError.

Other ways to write it

Using zip()

Using zip()
names = ["Riya", "Arjun", "Meera", "Kabir"]
marks = [88, 72, 95, 64]
result = dict(zip(names, marks))
print("Dictionary:", result)
Output
Dictionary: {'Riya': 88, 'Arjun': 72, 'Meera': 95, 'Kabir': 64}

zip() pairs the lists item by item, and dict() turns the pairs into a dictionary. This is the standard one-line way.

When the lists have different lengths

When the lists have different lengths
from itertools import zip_longest
names = ["Riya", "Arjun", "Meera"]
marks = [88, 72]
print("zip(): ", dict(zip(names, marks)))
print("zip_longest():", dict(zip_longest(names, marks, fillvalue="absent")))
Output
zip():         {'Riya': 88, 'Arjun': 72}
zip_longest(): {'Riya': 88, 'Arjun': 72, 'Meera': 'absent'}

zip() stops at the end of the shorter list, so Meera is silently dropped, while zip_longest() keeps going and fills the gap with fillvalue.

Try it yourself

Make a dictionary from ["a", "b", "c"] and [1, 2, 3], then swap the lists so the numbers become the keys.

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