Lists are mutable ordered and indexed collections of objects.
We can change, add, or remove items in a list after it has been created. Items can be of any data type, such as numbers, strings, or other objects.
Lists are formed by placing a comma-separated list of expressions in square brackets.
my_list = ["Hello", "World", 1, 2]
Accessing list items
We can access the items in a list by using their index values, which start from 0 for the first item. We can also use negative indexes to access the items from the end of the list.
For example:
print(my_list[0]) # prints "Hello"
print(my_list[-1]) # prints 2
Nested lists
We can also add lists within another list.
my_list = [ [0, 1, 3], ['a', 'b', 'c'], ['red', 'yellow', 'blue'] ]
print(new_list[2][1]) # prints yellow
Slicing of a List
Using slicing, we can print a specific range of elements from a list. The python list ‘Slice’ operation is used to print a specific range of elements; it is denoted by the ‘Colon (:)’. To print the elements from a specific range, use the start index tag (:index) to specify the last range element until which we want to specify (index:).
my_list = ['A', 'E', 'I', 'O', 'U']
print(my_list[1:4]) # prints ['E', 'I', 'O']
Looping through a list
We can loop through a list using the 'in' keyword:
my_list = ['red', 'blue', 'green', 'black']
for thing in my_list:
print(thing)
List concatenation
We can join multiple lists using '+' operator:
a = [0, 1, 2, 3, 4]
b = [5, 6, 7, 8, 9]
c = a + b
print(c) # prints [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
Multiple concatenation
We can return a sequence self-concatenated specified amount of times using '*' operator:
a = [0, 1]
b = a * 3
print(b) # prints [0, 1, 0, 1, 0, 1]
List Comprehension
A list comprehension consists of an expression followed by the for statement inside square brackets.
numbers = [n*n for n in range(1, 6)]
print(numbers) # prints [1, 4, 9, 16, 25]
Using Lists as Stacks
The list methods make it very easy to use a list as a stack, where the last element added is the first element retrieved (“last-in, first-out”). To add an item to the top of the stack, use append(). To retrieve an item from the top of the stack, use pop() without an explicit index. For example:
stack = [3, 4, 5]
stack.append(6)
stack.append(7)
print(stack) # prints [3, 4, 5, 6, 7]
stack.pop() # 7
stack.pop() # 6
stack.pop() # 5
print(stack) # prints[3, 4]
List methods
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len(list)
It gives the overall length of the list.
my_list = ['A', 'E', 'I', 'O', 'U'] print(len(my_list)) # prints 5 -
append()
Adds one element to the end of the list.
my_list = ['A', 'E', 'I', 'O'] my_list.append('U') print(my_list) # prints ['A', 'E', 'I', 'O', 'U'] -
insert()
Adds a component at the required position.
my_list = ['A', 'E', 'I', 'O'] my_list.insert(2,'U') print(my_list) # prints ['A', 'E', 'U', 'I', 'O'] -
extend()
Adds multiple elements to a list from another list.
a=[1,2] b=[3,4] a.extend(b) print(a) # prints [1, 2, 3, 4] -
pop()
Removes the element at the required position.
my_list = ['A', 'E', 'I', 'O', 'U'] my_list.pop(2) print(my_list) # prints ['A', 'E', 'O', 'U']Without any argument passed, it will remove element from the end of the list
my_list = ['A', 'E', 'I', 'O', 'U'] my_list.pop() print(my_list) # prints ['A', 'E', 'I', 'O'] -
remove()
Remove the first item from the list whose value is equal to given argument.
It raises a ValueError if there is no such item.
my_list = ['A', 'E', 'I', 'O', 'U'] my_list.remove('I') print(my_list) # prints ['A', 'E', 'O', 'U'] -
del()
We can also use the del statement to remove one or more items from a list.
a = [3, 2, 3, 8, 3, 4, 5, 6, 1, 2] del a[1] # deleting the second item print(a) # prints [3, 3, 8, 3, 4, 5, 6, 1, 2] del a[-1] # deleting the last item print(a) # [3, 3, 8, 3, 4, 5, 6, 1] del a[0 : 2] # delete first two items print(a) # prints # [8, 3, 4, 5, 6, 1] -
sort()
Sorts the list in ascending order.
my_list = [8, 1, 5, 3, 7] my_list.sort() print(my_list) # prints [1, 3, 5, 7, 8]To sort descending order:
my_list = [8, 1, 5, 3, 7] my_list.sort(reverse = True) print(my_list) # prints [8, 7, 5, 3, 1] -
reverse()
Reverses the order of the list.
my_list = ['A', 'E', 'I', 'O', 'U'] my_list.reverse() print(my_list) # prints ['U', 'O', 'I', 'E', 'A'] -
index()
Returns the first appearance of a particular value.
It raises a ValueError if there is no such item.
my_list = ['A', 'E', 'I', 'O', 'U'] print(my_list.index('O')) # prints 3 -
count()
Returns the number of elements with the required value.
my_list = [3, 4, 4, 1, 2, 3, 8, 3] print(my_list.count(4)) # prints 2 print(my_list.count(3)) # prints 3 -
max(list)
It returns an item from the list with a max value.
a = [3, 2, 3, 8, 3] print(max(a)) # prints 8 -
min(list)
It returns an item from the list with a min value.
a = [3, 2, 3, 8, 3] print(min(a)) # prints 2 -
copy()
Returns a duplicate (Shallow Copy) of the list.
a = [3, 2, 3, 8, 3] b=a.copy() print(b) # print [3, 2, 3, 8, 3]We can also copy (Deep Copy) using '=':
a = [3, 2, 3, 8, 3] b=a print(b) # prints [3, 2, 3, 8, 3] a.pop() print(b) # prints [3, 2, 3, 8] -
clear()
Removes all the elements from the list.
a = [3, 2, 3, 8, 3] a.clear() print(a) # prints []
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