The enumerate Function in Python

Today we’ll be talking about the enumerate function. We use it, for example, if we need both the elements of a sequence and their indices.

The enumerate function generally takes one or two parameters. The first parameter is the iterable that you want to iterate over and the second, optional parameter is the counter start value, so the initial value, starting from which the counting will be carried on.

Let’s define a list of students to illustrate how the function works:

>>> students = ['Sam', 'Joe', 'Bill', 'Annie']

Here they are, waiting to be enumerated.

Now let’s use the list to create an enumerate:

>>> enumerateStudents = enumerate(students)

You can check the type of enumerateStudents. It’s an enumerate.

>>> type(enumerateStudents)
<class 'enumerate'>

Using the list and tuple functions, you can convert an enumerate to a list or tuple respectively. Let’s use the former function first:

>>> list(enumerateStudents)
[(0, 'Sam'), (1, 'Joe'), (2, 'Bill'), (3, 'Annie')]

And now suppose we need some more students and we want them to be counted from index 4. This is what the second parameter in the enumerate function is for. Let’s create a list with the other students and then an enumerate:

>>> more_students = ['Jane', 'Martha', 'Lucy']
>>> enumerateMoreStudents = enumerate(more_students, 4)

You can see the three students here.

This time let’s convert the enumerate to a tuple:

>>> tuple(enumerateMoreStudents)
((4, 'Jane'), (5, 'Martha'), (6, 'Lucy'))

The enumerate Function in Loops

In a similar way as how we iterate over the keys and values of a dictionary, you can use the enumerate function to retrieve the indices and their corresponding values from sequences:

>>> name = "David"
>>> for i, v in enumerate(name):
...     print("{} - {}".format(i, v))
... 
0 - D
1 - a
2 - v
3 - i
4 – d

In the example above we used the enumerate function with just one argument, so the counting starts at 0. But you can set the initial index to a different value:

>>> for i, v in enumerate(name, 101):
...     print("{} - {}".format(i, v))
... 
101 - D
102 - a
103 - v
104 - i
105 - d

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OK, that’s it for today.

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Do you know any interesting use cases for the enumerate function? If you do, write them down in the comments.