Python - List Methods
Python
In this tutorial we will learn about list methods in Python.
In the previous tutorial Python - List we learned about lists. Feel free to check that out.
Quick recap
- A list is an ordered sequence of items.
- We create lists in Python using the
[ ]. - Items inside the list are indexed.
- Indexing starts from 0.
Alright, let's get started with list methods.
append
We use the append method to append the passed object to a list.
In the following Python program we are appending objects to a list.
# list
myList = []
print("Starting", myList)
# append integer
myList.append(1)
# append float
myList.append(3.14)
# append string
myList.append("Yusuf Shakeel")
# append complex number
myList.append((2+3j))
# append boolean
myList.append(True)
# append list
myList.append([1,2,3])
# output
print("Final", myList)
The above Python code will give use the following output.
Starting []
Final [1, 3.14, 'Yusuf Shakeel', (2+3j), True, [1, 2, 3]]
clear
We use the clear method to remove all the items from a given list.
In the following Python code we are removing all the items from the list.
# list
myList = [1, 2, 3]
print("before", myList)
# clear
myList.clear()
# output
print("after", myList)
The above code will give the following output.
before [1, 2, 3]
after []
copy
We use the copy method to make a copy of an existing list.
In the following Python program we are creating a copy of a given list.
# list
myList = [1, 2, 3]
# copy
newList = myList.copy()
# output
print(newList)
count
We use the count method to find the total number of times a given object appears in a given list.
In the following Python program we are checking the number of times the given items appear in the list.
# list
myList = [1, 2, 3, 2, 4, "Hello", "Happy", "happy", "hello"]
# count
print(myList.count("unknown")) # 0
print(myList.count("Hello")) # 1
print(myList.count("happy")) # 1
print(myList.count(2)) # 2
extend
We use the extend method to append a sequence of items to an existing list.
It does not returns any value. It simply appends the sequence.
In the following Python program we are appending fruitList to vegList.
# list
vegList = ["Tomato", "Onion", "Potato", "Broccoli", "Lettuce"]
print("before", vegList)
# second list
fruitList = ["Apple", "Mango", "Orange", "Guava", "Watermelon"]
# extend
vegList.extend(fruitList)
# output
print("after", vegList)
We get the following output for the above code.
before ['Tomato', 'Onion', 'Potato', 'Broccoli', 'Lettuce']
after ['Tomato', 'Onion', 'Potato', 'Broccoli', 'Lettuce', 'Apple', 'Mango', 'Orange', 'Guava', 'Watermelon']
index
We use the index method to get the first occurrence of a given value in a list.
On success, this method returns the index of the item. If the item is not found then it gives an exception.
In the following Python program we are finding 6 in the given list.
# list
myList = [1, 2, 5, 6, 4, 3, 6, 7, 9, 8]
# index
print(myList.index(6)) # 3
The above code will give us 3 as the first occurrence of digit 6 is at index 3.
Note! Even though we have 6 appearing twice in the list but the index method will return the index were it first encountered 6.
insert
We use the insert method to insert an object at a specific index in the list.
Here are the possible ways we can insert item in a list.
Insert at the start
Following is the syntax to insert an item at the start (0th index) of the list.
list.insert(0, item)
Where, list is a variable that holds the list and item is the item that is getting inserted in the list at the start (0th index).
Note! Item present at the specific index is not delete but shifted to make room for the new item.
In the following Python program we are inserting string "Happy" at index 0 (start of the list).
# list
myList = [1, 2, 3, 4, 5]
print("before", myList)
# insert
myList.insert(0, "Hello")
# output
print("after", myList)
The above code will give use the following output.
before [1, 2, 3, 4, 5]
after ['Hello', 1, 2, 3, 4, 5]
Note! In the above output we can see that item 1 is moved from index 0 and it's position is taken by the inserted item "Hello".
Insert at the end
Following is the syntax to insert an item at the end of the list.
list.insert(len(list), item)
We use the len method to get the total number of items in the list.
In the following Python program we are inserting string "Happy" at the end of the list.
# list
myList = [1, 2, 3, 4, 5]
print("before", myList)
# insert
myList.insert(len(myList), "Hello")
# output
print("after", myList)
The above code will give use the following output.
before [1, 2, 3, 4, 5]
after [1, 2, 3, 4, 5, 'Hello']
If we set the insert index to a value greater than the total item present in the list then the new item will be inserted at the end.
In the following Python program the new item is inserted at the end of the list.
# list
myList = [1, 2, 3, 4, 5]
print("before", myList)
# insert
myList.insert(100, "Hello")
# output
print("after", myList)
We will get the following output.
before [1, 2, 3, 4, 5]
after [1, 2, 3, 4, 5, 'Hello']
Insert between start and end
If we give any index that falls between the start and the end index of the list then the new item will be inserted somewhere within the list.
In the following Python program we have a list of 5 numbers and we are inserting the string "Hello" somewhere in between.
# list
myList = [1, 2, 3, 4, 5]
print("before", myList)
# insert
myList.insert(3, "Hello")
# output
print("after", myList)
The above Python program will give us the following output.
before [1, 2, 3, 4, 5]
after [1, 2, 3, 'Hello', 4, 5]
pop
We use the pop method to pop items from the list.
This method returns the popped item.
If we don't pass any index then pop method will pop the last item from the list.
In the following Python program we are popping out the last item from the given list.
# list
myList = [1, 2, 3, 4, 5]
print("before pop:", myList)
# pop
x = myList.pop()
# output
print("Pop", x)
print("after pop:", myList)
We get the following output.
before pop: [1, 2, 3, 4, 5]
Pop 5
after pop: [1, 2, 3, 4]
We can also pop items from a specific index using the following syntax.
list.pop(index)
In the following Python program we are popping out item at index 3.
# list
myList = [1, 2, 3, 4, 5]
print("before pop:", myList)
# pop
x = myList.pop(3)
# output
print("Pop", x)
print("after pop:", myList)
The above Python program will give us the following output.
before pop: [1, 2, 3, 4, 5]
Pop 4
after pop: [1, 2, 3, 5]
remove
We use the remove method to remove an item from the list.
Syntax
list.remove(item)
In the following Python program we are removing 3 from the list.
# list
myList = [1, 2, 3, 4, 5]
print("before", myList)
# remove
myList.remove(3)
# output
print("after", myList)
Output:
before [1, 2, 3, 4, 5]
after [1, 2, 4, 5]
reverse
We use the reverse method to reverse the order of the items in the list.
In the following Python program we are reversing the order of the items in the list.
# list
myList = [1, 2, 3, 4, 5]
print("before", myList)
# reverse
myList.reverse()
# output
print("after", myList)
We will get the following output.
before [1, 2, 3, 4, 5]
after [5, 4, 3, 2, 1]
sort
We use the sort method to sort the items of a list in ascending and descending order.
By default the items are sorted in ascending order.
In the following Python program we are sorting the items of the list in ascending order.
# list
myList = [1, 10, 9, 6, 3, 8, 2, 5, 4, 7]
print("before", myList)
# sort
myList.sort()
# output
print("after", myList)
We will get the following output.
before [1, 10, 9, 6, 3, 8, 2, 5, 4, 7]
after [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
To sort the item in descending order we use the following syntax.
list.sort(reverse=True)
In the following Python program we are sorting the items of the list in descending order.
# list
myList = [1, 10, 9, 6, 3, 8, 2, 5, 4, 7]
print("before", myList)
# sort
myList.sort(reverse=True)
# output
print("after", myList)
The above Python program will give use the following output.
before [1, 10, 9, 6, 3, 8, 2, 5, 4, 7]
after [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]