Adding and removing items from a list in Python
problem
You are using a list in your Python program and wish to add and remove items. In this post we will see built-in functions that allow us to manipulate the items in the list.
SOLUTION
Adding an item
Let’s suppose we have a list named numbers that is currently empty as follows:
numbers = [] # empty list
We can also create an empty list using the list() function as follows:
numbers = list() # creates an empty list
We wish to add a number, e.g. 5.
numbers.append(5) # adds it to the end of the list
Let’s add another number, e.g. 7
numbers.append(7)
Let’s print the list
print(numbers)
output
append() adds the item to the end of the list.
Adding an item at the beginning
Let’s suppose I wish to add number 3 at the beginning, I’ll use the insert() function:
numbers.insert(0,3) # adds the number 3 at index 0
output
The insert() function takes 2 parameters:
- the index where to insert the new item
- and the second parameter is the item to be added.
Recap: In Python’s list we can have items of any data-type.
Adding multiple items
We can use append() again to add a list of items, for example:
numbers.append([9,11,13]) # add the list [9,11,13] to the current list
output
The list now contains 4 items: 3 integers and one list.
We can use len() to determine the size of the list, for example:
len(numbers)
output
Removing an item
To remove the last item of the list we can use the pop() function. For example:
removed_item = numbers.pop() # removes and returns the last item
print(removed_item)
output
The last item was the list [9,11,13] added above. The pop() function removes and returns the item in case we wish to further use it we store it in a variable (removed_item).
Remove item by index
Currently the list contains the following items:
The pop() function can accept a parameter which acts as the index of the item to be removed. For example to remove the second item:
second_item = numbers.pop(1) # remove and get the second item
print(second_item)
output
Removing an item using its value
Let’s suppose we wish to remove number 7 from the list. We can use the remove() function with a parameter being the item to be removed. For example:
numbers.remove(7)
It’s important to note here that the remove() function does not return the item, only removes it.
output
The list now contains only one item: 3.
Attempting to Remove an item that does not exist
Using the remove() with an item that is not in the list will result in a ValueError.
Such errors that crash the program can be handled using the try catch statement.
conclusion
In this post we saw two ways for adding items in a list and three ways for removing items from a list and their possible errors.
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Ellion
Professional IT consultant, writer, programmer enthusiast interested in all sorts of coding.
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