Python – how to use enumerate to get index and value

The Python enumerate() function is a powerful tool for looping through sequences while keeping track of the index of the current item. It transforms any iterable (like a list, tuple, or string) into an enumerate object, which yields pairs of (index, value).

This article will show you how to effectively use enumerate() to simplify your code and make your loops more readable. We’ll cover basic usage, starting indices, and practical examples to illustrate its versatility.

Basic Usage of enumerate()

The most straightforward use of enumerate() involves iterating through a list and accessing both the index and value of each element.

 fruits = ['apple', 'banana', 'cherry']
 

 for index, fruit in enumerate(fruits):
  print(f"Index: {index}, Fruit: {fruit}")
 

 Index: 0, Fruit: apple
 Index: 1, Fruit: banana
 Index: 2, Fruit: cherry
 

In this example, enumerate(fruits) returns an iterator that yields pairs. The loop unpacks each pair into index and fruit, allowing you to use both within the loop. This avoids the need for manual index management.

Starting the Index from a Different Number

By default, enumerate() starts the index at 0. However, you can specify a different starting value using the start parameter.

 fruits = ['apple', 'banana', 'cherry']
 

 for index, fruit in enumerate(fruits, start=1):
  print(f"Position: {index}, Fruit: {fruit}")
 

 Position: 1, Fruit: apple
 Position: 2, Fruit: banana
 Position: 3, Fruit: cherry
 

Here, enumerate(fruits, start=1) begins the index at 1, which can be useful when you want to display item positions in a more human-readable format.

Using enumerate() with Strings

enumerate() works equally well with strings, allowing you to iterate through the characters of the string and their corresponding indices.

 word = "Python"
 

 for index, char in enumerate(word):
  print(f"Index: {index}, Character: {char}")
 

 Index: 0, Character: P
 Index: 1, Character: y
 Index: 2, Character: t
 Index: 3, Character: h
 Index: 4, Character: o
 Index: 5, Character: n
 

This is helpful for tasks like character-by-character processing or finding the position of a specific character.

Using enumerate() with Tuples

Tuples are another common iterable type that can be used with enumerate().

 colors = ('red', 'green', 'blue')
 

 for index, color in enumerate(colors):
  print(f"Index: {index}, Color: {color}")
 

 Index: 0, Color: red
 Index: 1, Color: green
 Index: 2, Color: blue
 

This example demonstrates how enumerate() can be applied to tuples in the same way as lists.

Conditional Logic with enumerate()

You can combine enumerate() with conditional statements to perform actions based on the index or value of an element.

 numbers = [10, 20, 30, 40, 50]
 

 for index, number in enumerate(numbers):
  if index % 2 == 0:
  print(f"Even index {index}: {number}")
  else:
  print(f"Odd index {index}: {number}")
 

 Even index 0: 10
 Odd index 1: 20
 Even index 2: 30
 Odd index 3: 40
 Even index 4: 50
 

In this example, the code checks if the index is even or odd and prints a different message accordingly.

Finding Specific Elements with enumerate()

enumerate() can be used to find the index of a specific element within a list.

 names = ['Alice', 'Bob', 'Charlie', 'David']
 

 target_name = 'Charlie'
 

 for index, name in enumerate(names):
  if name == target_name:
  print(f"{target_name} found at index {index}")
  break
 

 Charlie found at index 2
 

This code iterates through the list of names and prints the index when it finds the target name.

Using enumerate() in List Comprehensions

enumerate() can also be incorporated into list comprehensions for concise and efficient code.

 words = ['hello', 'world', 'python']
 indexed_words = [f"{index}: {word}" for index, word in enumerate(words)]
 print(indexed_words)
 

 ['0: hello', '1: world', '2: python']
 

This example creates a new list where each element is a string combining the index and the original word.

Practical Example: Modifying a List Based on Index

Let’s consider a practical example where you want to modify a list based on the index of its elements. Suppose you want to double the value of elements at even indices.

 numbers = [1, 2, 3, 4, 5, 6]
 

 for index, number in enumerate(numbers):
  if index % 2 == 0:
  numbers[index] = number * 2
 

 print(numbers)
 

 [2, 2, 6, 4, 10, 6]
 

This code iterates through the numbers list and doubles the value of elements at even indices, modifying the list in place.