The Enumerate Function#

In this tutorial, we will explore the enumerate() function in Python, which is a valuable tool for working with sequences like lists, tuples, and strings. This tutorial is designed for humanists and those new to Python, so we’ll use simple examples with strings to help you understand the concept.

It is important to remember that enumerate() can be replaced with longer, more verbose code. Enumerate() is useful, however, in making your code quicker to write. It allows for you to do something in a single line that would otherwise take 3 lines to write.

While enumerate() can look a bit daunting on the surface, it is worthwhile to learn. Not only will it make your code look more professional, it will also allow you to better understand someone else’s code. You will frequently see it used in code samples without explanation.

What is the enumerate() function?#

The enumerate() function is a built-in Python function that allows you to iterate over a sequence (like a list or a string) and keep track of the index (position) of the current item along with the item itself. This can be particularly useful when you need to know the position of an item in a sequence while processing it.

The basic syntax of the enumerate() function is:

enumerate(sequence, start=0)

  • sequence: The sequence you want to iterate over (e.g., a list, tuple, or string).

  • start: An optional parameter that specifies the starting value of the index (default is 0).

The enumerate() function returns an iterator, which you can use with a for loop.

Using the enumerate() function with strings#

Let’s say you have a string and you want to print each character in the string along with its index. You can use the enumerate() function to achieve this.

text = "William"

for index, character in enumerate(text):
    print(index, character)

0 W
1 i
2 l
3 l
4 i
5 a
6 m

As you can see, the enumerate() function makes it easy to keep track of the index of each character in the string.

Changing the starting index with the start parameter#

By default, the enumerate() function starts the index at 0. However, you can change the starting index by providing a value for the start parameter.

For example, let’s start the index at 1:

text = "William"

for index, character in enumerate(text, start=1):
    print(index, character)

1 W
2 i
3 l
4 l
5 i
6 a
7 m

As you can see, the index now starts at 1 instead of 0.

Practical example: Finding the positions of a specific character in a string#

Let’s use the enumerate() function in a practical example. Suppose you want to find the positions of all occurrences of the letter “l” in a string.

text = "l"
target = "l"

positions = []

for index, character in enumerate(text):
    if character == target:
        positions.append(index)

print(f"The character '{target}' is found at positions: {positions}")

The character 'l' is found at positions: [0]

In this example, the enumerate() function helps us keep track of the index while iterating through the string. We check if the current character matches the target character, and if it does, we add the index to our positions list.