How to Modify an Item Within a List in Python

In this tutorial, you will learn how to modify an element of a Python list.

TLDR solution

z = [e0, e1, e3]

# append a an element
z.append(e4)

# delete an element (y)
z.pop(index_y)

# replace a single element
z[index_y] = new_value

# replace all occurences of a value using list comprehension
z = [new_value if x == y else x for x in z]

Add an Element to a List

Suppose, you want to append mackerel to list of fishes:

fish = ['salmon', 'pufferfish', 'shark']

fish.append('mackerel')

print(fish)

The new list:

['salmon', 'pufferfish', 'shark', 'mackerel']

Delete an Element from a List

Let's undo the addition by popping the element out of the list:

# specify the index of the element you want to remove
fish.pop(3)
print(fish)

The output:

['salmon', 'pufferfish', 'shark']

Suppose, you want to change the first element (salmon) of the fish list to mackerel. If it's a small list, you can just select the element and assign the new value. Otherwise, it is more convenient to use a list comprehension:

fish = ['salmon', 'pufferfish', 'shark']

# select element and assign value
fish[0] = 'mackerel'

# or use list comprehension
fish = ['mackerel' if x == 'salmon' else x for x in fish]

print(fish)

Note that indices start at 0. The output:

['mackerel', 'pufferfish', 'shark']

That's it! You just learned how to modify a list in Python.