What is a List?
In python list is a collection of items in a particular order. lists are like a container where we can store multiple values of any type. For creating a list in Python we use [] - square brackets, opening square brackets indicate the start of a list, and closing square brackets indicate the end of a list. We can store values of any type in a list, values of a list are known as elements and each element is separated by ,. This is how a simple python list looks like ['apple', 'grapes', 'banana', 'orange', 'guava'] . Unlike string or tuple lists are mutable which means we can modify a list. Here are a few examples of valid lists in python.
# this is how we create a new list in python
list1 = [] # this is an empty list
# this is another way to create a new list in python
list1 = list() # this is an empty list
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava'] # list of strings
even_numbers = [2,4,6,8,10] #list of numbers
vowels = ['a','e','i','o','u'] #list of characters
list2 = ['hello', "2", 76, 8.23] #list of mixed values
list3 = ["How are You", ["hi", 4.5, 9], 98] #list of mixed values
Accessing Element of a list.
Lists are ordered collections of elements, each and every element in a list has its own index and we can use this index to access and modify elements of the list. Indexing starts from 0 and goes up to a length of the list -1. Here is a quick diagram of how indexing works.
Accessing Individual Elements of a list
To access an element of a list we write the name of the list followed by the index of the elements enclosed in square brackets. This is also known as indexing.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
# using forward indexing
fruits[0] #o/p ->'apple'
fruits[1] #o/p ->'grapes'
fruits[2] #o/p ->'banana'
fruits[3] #o/p ->'orange'
fruits[4] #o/p ->'guava'
# using backward indexing
fruits[-1] #o/p ->'guava'
fruits[-2] #o/p ->'orange'
fruits[-3] #o/p ->'banana'
fruits[-4] #o/p ->'grapes'
fruits[-5] #o/p ->'apple'
# using the element of a list in a simple sentence
message = "I like " + fruits[0] + " more than " + fruits[3]
print(message) # -> I like apple more than orange
Accessing a range of Elements from a list(list slicing).
When we want to access a range of elements from a list we use list slicing, and we use list slicing when we have to work with a specific part of the list. For using list slicing we use a similar syntax to list indexing, instead of passing the index only we pass three parameters inside the square brackets list_name[start_index:stop_index:step_value], step_value is optional and the default value for step_value is 1. one more thing to keep in mind is that stop_index is exclusive. Here are a few examples of list slicing.
alphabets = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
# it returns a new list with elements from index 10 to index 19, we don't get an element at index 20 because the stop_index is exclusive
alphabets[10:20] #o/p -> ['k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't']
# when we pass the step_value of 2, we get a new list of every second element from index 10 to index 19.
alphabets[10:20:2] #o/p -> ['k', 'm', 'o', 'q', 's']
# this will return a new list of the first 10 elements starting from index 0
alphabets[:10] # o/p -> ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j']
# this will return a new list of elements starting at index 10 till the end of the list
alphabets[10:] # o/p -> ['k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
# this will return a new list with every second element
alphabets[::2] # o/p -> ['a', 'c', 'e', 'g', 'i', 'k', 'm', 'o', 'q', 's', 'u', 'w', 'y']
# this will return a copy of the complete list
alphabets[:] # o/p -> ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
Modifying Element of a list
modifying a list is very similar to accessing a list, we use list indexing and list slicing to modify a list. Here are a few examples of modifying a list.
# modifying a single element
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
fruits[1] = "mango" # this will change the element at index 1 to mango
print(fruits) #o/p ['apple', 'mango', 'banana', 'orange', 'guava']
# modifying multiple elements at a time
fruits[0:3] = ['Coconut', 'Pear', 'Dates'] # this will change elements at index 0,1and 2 to Coconut, Pear, Dates
print(fruits)
Using the Membership operator with a list
we can use in and not in operators with a list, we use in and not in operators to check if the element is present in the list or not.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
'apple' in fruits
# o/p ->True because apple is present in the list
'mango' in fruits
#o/p ->False because mango is not present in the list
'apple' not in fruits
#o/p -> False because apple is present in the list
'mango' not in fruits
#o/p -> True because mango is not present in the list
Using a Comparison operator with a list
we can use a comparison operator like <,>,==,!= to compare two lists in python. When we compare two lists using the comparison operator, python compares each and every element of a list in lexicographical order.
list1 = [10,20,30,40,50,60]
list2 = [10,20,30,40,50,60]
print(list1 == list2) #o/p -> True because each and every element of the list are same
list1 = [10,20,30,40,50,60]
list2 = [10,20,70,40,50,60]
print(list1 == list2) #o/p -> False because each and every element of the list are not same
list1 = [10,20,30,40,50,60]
list2 = [10,20,70,40,50,60]
print(list1 != list2) #o/p -> True
list1 = [10,20,30,40,50,60]
list2 = [10,20,70,40,50,60]
print(list1 < list2) #o/p -> True because third element of list1 is less than third element of list2
list1 = [10,20,30,40,50,60]
list2 = [10,20,70,40,50,60]
print(list1 > list2) #o/p -> False
using + and * with the Python list
we can use the concatenation operator and replication operator with the python list. Here are a few examples.
list1 = [10,20,30,40,50,60]
list2 = [70,80,90,100]
print(list1 + list2) #o/p -> [10, 20, 30, 40, 50, 60, 70, 80, 90, 100]
list1 = [10,20,30,40,50,60]
print(list1 *2) #o/p -> [10, 20, 30, 40, 50, 60, 10, 20, 30, 40, 50, 60]
Length of a list
In python, we use the len() function to find the length of a list. len() function tells us the number of elements in a list. This is how we use the len() function to find the length of a list.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
print(len(fruits)) # o/p -> 5
list1 = [10,20,30,40,50,60]
list_length = len(list1)
print(list_length) # o/p -> 6
Traversing a list.
Traversing a list means processing each and every element of a list. We use a loop to traverse a list.
#syntax
for variable_name in your_list:
#do something
#In each iteration value from your list will be assigned to variable_name and you can process that value in the way you want.
Example:-
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
for fruit in fruits:
print(fruit) # in each iteration fruit variable will be assigned a new value from the fruits list and I am printing that value.
#output
apple
grapes
banana
orange
guava
If we want to use the index of the elements to access them, then we can use the range() and the len() functions.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
#syntax
# for variable_name in range(len(your_list)):
# #do something
# your_list[variable_name]
for index in range(len(fruits)):
print(index) # in each iteration index variable will be assigned the index of the elements from the fruits variable.
#output
0
1
2
3
4
for index in range(len(fruits)):
print(fruits[index]) # this line prints the values from the fruits list from the passed index. this is the same as using the index to access individual elements from a list.
#output
apple
grapes
banana
orange
guava
Python List Methods
Python comes with some built-in methods and functions. In this part of the article, we are going to learn about built-in methods of lists.
list.append(element)
append method add a new element at the end of the list.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
fruits.append('pear')
print(fruits) # o/p -> ['apple', 'grapes', 'banana', 'orange', 'guava', 'pear']
list.extend(iterable)
extend method extends the list by adding all the elements from the iterable to the list.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
another_fruits_list = ['pear','kiwi','coconut']
fruits.extend(another_fruits_list)
print(fruits)
# o/p -> ['apple', 'grapes', 'banana', 'orange', 'guava', 'pear', 'kiwi', 'coconut']
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
another_fruits_tuple = ('pear','kiwi','coconut')
fruits.extend(another_fruits_tuple)
print(fruits)
# o/p -> ['apple', 'grapes', 'banana', 'orange', 'guava', 'pear', 'kiwi', 'coconut']
list.insert(index,element)
insert method takes two arguments, the first one is index and the second one is element. We use the insert method when we want to add a new element at a specific index in a list. insert method add the element at the given index and shift the other element to the right by one position.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
fruits.insert(1,'pear') # i want to add pear at index 1
print(fruits)
# o/p -> ['apple', 'pear', 'grapes', 'banana', 'orange', 'guava']
list.pop(index) / list.pop()
the pop method is used to remove elements from the list, the pop method takes the index as an optional argument if we use list.pop(index_of_item_you_want_to_remove) then it removes the element from the list at the given index and returns it and if we use list.pop() then it removes the last element of the list and returns it. the pop method returns the removed element, so you can use the removed element later.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
fruits.pop() # if no index is passed it removes the last element
print(fruits)
#o/-> ['apple', 'grapes', 'banana', 'orange']
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
popped_element = fruits.pop() # it returns the popped element, so we can store the popped element in a variable and use that later.
print(popped_element)
#o/p -> guava
print(fruits)
# o/p -> ['apple', 'grapes', 'banana', 'orange']
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
fruits.pop(1) # removes the element at index 1
print(fruits)
list.remove(element)
remove method is also used to remove elements from the list, but it takes an element as an argument and removes the element from the list and if there is a duplicate element in the list then it removes the first occurring element.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
fruits.remove('grapes')
print(fruits)
#o/p-> ['apple', 'banana', 'orange', 'guava']
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava', 'grapes']
fruits.remove('grapes') # grapes wat at two positions 1 and 5, 1 comes first so grapes at index 1 is removed
print(fruits)
#o/p-> ['apple', 'banana', 'orange', 'guava', 'grapes']
list.clear()
the list.clear() method removes all the elements from the list.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
fruits.clear()
print(fruits)
#o/-> []
list.count(element)
list.count() method takes an element as an argument and returns the number of times the element occurs in the list.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
element_count = fruits.count('grapes')
print(element_count)
#o/-> 1
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava','grapes']
element_count = fruits.count('grapes')
print(element_count)
#o/-> 2
list.sort()
This method is used to sort the list, by default this method sort the list in ascending order.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava','grapes']
fruits.sort()
print(fruits)
#o/-> ['apple', 'banana', 'grapes', 'grapes', 'guava', 'orange']
list.reverse()
This method is used to reverse the list.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava']
fruits.reverse()
print(fruits)
#o/-> ['guava', 'orange', 'banana', 'grapes', 'apple']
list.copy()
list.copy() method returns a copy of the original list. modifying the new list doesn't modify the original list.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava',]
copied_list = fruits.copy()
print(copied_list)
#o/-> ['apple', 'grapes', 'banana', 'orange', 'guava']
list.index(element)
list.index() method returns the index of the specified element if there is a duplicate element it returns the index of the first occurring element. It also takes two positional arguments list.index(element,start_index,stop_index), and returns the index of the element between start_index and stop_index.
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava',]
index = fruits.index('grapes')
print(index)
#o/-> 1
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava','grapes']
index = fruits.index('grapes')
print(index)
#o/-> 1
fruits = ['apple', 'grapes', 'banana', 'orange', 'guava','grapes']
index = fruits.index('grapes',2,6)
print(index)
#o/-> 5
Conclusion
That's it for this article, Write your feedback in the comment section.
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