How to Enumerate in Python: Step by Step

Materials Required: Latest version of Python (Python 3), an integrated development environment (IDE) of your choice (or terminal), and a stable internet connection

Prerequisites/helpful expertise: Basic knowledge of Python and programming concepts

Enumerate is a built-in Python function. It enables you to keep track of iterations, write more efficient loops, and access the index and values of an iterable object.

Glossary

What is enumerate in Python?

Python enumerate assigns a count to each item within an iterable and returns it as an enumerate object. This function enables you to loop over an iterable while accessing the index of items within it. For example, suppose you want to assign a count to each item in the following sequence:

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pokemon = ['Pikachu', 'Bulbasaur', 'Squirtle', 'Charmander']

In that case, you could feed this sequence to the function enumerate. The output will include your sequence with a counter, like this:

You can use enumerate with any iterable object in Python. Examples of iterable objects include lists, strings, tuples, and dictionaries.

Enumerate syntax

By default, the syntax of Python enumerate is as follows:

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enumerate(iterable, start=0)

You can adjust the enumerate function to fit your needs by changing its parameters. Enumerate has two parameters:

1. Iterable: The iterable is the sequence, list, or objects you select to enumerate. This is a required parameter.

2. Start: The start value lets the enumerate function know which number to start counting from. This is an optional parameter. If you omit it, the start will be 0.

How to use enumerate in Python

Passing an iterable to enumerate() returns an enumerated object that you can iterate through with a for loop or convert to alist of tuples using the list() method. This function may be helpful anytime you want to keep count of or access iterable items. In the following sections, we’ll examine how the enumerate function works with lists, dictionaries, tuples, strings, for loops, and in reverse.

How to enumerate a list in Python

Here’s how the enumerate function works with a list as the iterable and a start value of 0 (the default):

enumerate() takes a list called "fruits" as an argument and returns an enumerate object, which contains pairs of indices and corresponding items from the list. The for loop unpacks each pair into i and fruit variables, where i is the index and fruit is the corresponding item.

Try it yourself

Try writing a program that returns the following output:

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programs = ['python','c','react','javascript','bash']

for i, program in enumerate(programs,1):
  print(i, program)

How to enumerate a dictionary in Python

There are two ways to enumerate a dictionary in Python. The first method will only assign a counter to the keys of a dictionary, not the values:

This method returns a list of the keys in the dictionary, which can then be passed to enumerate() just like in our example with the list. The rest of the code works the same way.

The second technique uses the items() function to assign a counter or a count variable to both the keys and the values in a dictionary:

The .items() method returns a list of key-value pairs from the dictionary, which can then be passed to enumerate(). The for loop unpacks each pair into fruit and color variables, where fruit is the key and color is the corresponding value.

Try it yourself

Try using enumerate to add a counter to the keys of this dictionary:

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pokemon = {'Pikachu': 'Electric', 'Bulbasaur': 'Grass/Poison', 'Squirtle':'Water', 'Charmander':'Fire'}

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for i, creature in enumerate(pokemon.keys()):
  print(i,creature)

Now, try adding items() to add a counter to the values in the same dictionary:

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for i, (creature, pokemon_type) in enumerate(pokemon.items()):
  print(i,creature,pokemon_type)

How to enumerate a tuple in Python

To enumerate a tuple in Python, you’ll approach it the same way you would enumerate a list:

The code works in the same way as the previous examples with a list, except that a tuple is used instead. enumerate takes a tuple as an argument and returns an enumerate object, which contains pairs of indices and corresponding items from the tuple.

However, if you need to use enumerate to iterate through a list of tuples, you’ll write it a little differently:

How to use enumerate a Python for loop

The enumerate function can help you write cleaner, more efficient for loops in Python. Without it, you would need to loop over the range of the iterable and increment the counter yourself. Although both methods achieve the same effect, enumerate is more straightforward and readable. Here is a side-by-side comparison:

Without enumerate:

Here, the range function generates a sequence of indices from 0 to len(fruits) - 1 (2 in this case). The for loop iterates over these indices and uses each index i to obtain the corresponding item fruit from the list fruits.

With enumerate:

This code is the same as the previous example, but it uses the enumerate function instead of the range function. enumerate takes the list fruits as an argument and returns an enumerate object, which contains pairs of indices and corresponding items from the list.

Try it yourself

Try rewriting this for loop with enumerate:

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pokemon = ['Pikachu', 'Bulbasaur', 'Squirtle', 'Charmander']
for i in range(len(pokemon)):
    current_pokemon = pokemon[i]
    print(i, current_pokemon)

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for i, current_pokemon in enumerate(pokemon):
  print(i, current_pokemon)

How to enumerate a string in Python

Since strings are iterable in Python, they can be passed to the enumerate function as well. Enumerating a string will return its index and value pairs. Here’s an example using enumerate on a string starting from 1:

Try it yourself

Try using enumerate on the following string to return an object that begins with 5:

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string = "This is a test string."

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string = "This is a test string."
for index, char in enumerate(string, start=5):
  print(index, char)

How to enumerate in reverse order in Python

You can’t reverse the type of object that the enumerate function returns. However, you can reverse the order by converting the enumerate object into a list or tuple first. You’ll accomplish this by using Python’s list() or tuple() and reversed() functions. Here’s an example:

Try it yourself

Can you use enumerate in reverse order to put the list languages in order from 5 to 1?

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languages = ['Python', 'Java', 'C++', 'JavaScript', 'C#']

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enumerated_languages = tuple(enumerate(languages, 1))
reversed_languages = reversed(enumerated_languages)

for index, value in reversed_languages:
  print(index, value)

Key takeaways

• The enumerate function adds a counter to an iterable and returns it as an enumerate object.
• Enumerate has two parameters: the iterable and the start value.
• You can use enumerate with any iterable in Python.
• You can reverse the order of enumeration by converting the enumerate object to a list or tuple and reversing it.
• Enumerate lets you access both the index and the value simultaneously.

Resources

• Python built-in functions list official documentation
• Python looping techniques official documentation
• How to Use Python Break
• How to Use Range in Python
• How to Use For Loops in Python
• Python Loops Cheat Sheet

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