Python List

In this tutorial, we’ll learn everything about Python lists, how they are created, slicing off a list, including or expelling elements from them, so on.

Python offers a scope of compound data types often referred to as sequences. Rundown is one of the most much of the time used and flexible data types used in Python.

How to create a list?

In Python programming, a list is created by placing all the items (elements) inside square sections [], isolated by commas.

It can have any number of things and they might be of various kinds ((integer, float, string, etc.).

# empty list
my_list = []

# list of integers
my_list = [1, 2, 3]

# list with mixed data types
my_list = [1, "Hello", 3.4]

A list can also have another list as an item. This is called a nested list.

# nested list
my_list = ["mouse", [8, 4, 6], ['a']]

How to access elements from a list?

There are various ways in which we can access the elements of a list.

List Index

We can use the index operator [] to access an item in a list. In Python, indices start at 0. So, a list having 5 elements will have an index from 0 to 4.

Trying to access indexes other than these will raise an IndexError. The index must be an integer. We can’t use float or other types, this will result in TypeError.

Nested lists are accessed using nested indexing.

# List indexing

my_list = ['p', 'r', 'o', 'b', 'e']

# Output: p
print(my_list[0])

# Output: o
print(my_list[2])

# Output: e
print(my_list[4])

# Nested List
n_list = ["Happy", [2, 0, 1, 5]]

# Nested indexing
print(n_list[0][1])

print(n_list[1][3])

# Error! Only integer can be used for indexing
print(my_list[4.0])

p
o
e
a
5
Traceback (most recent call last):
  File "<string>", line 21, in <module>
TypeError: list indices must be integers or slices, not float

# Negative indexing in lists
my_list = ['p','r','o','b','e']

print(my_list[-1])

print(my_list[-5])

When we run the above program, we will get the following output:

e
p

How to slice lists in Python?

We can access a range of items in a list by using the slicing operator :(colon).

# List slicing in Python

my_list = ['w','o','r','l','d','o','f','i','t','e','c',h']

# elements 3rd to 5th
print(my_list[2:5])

# elements beginning to 4th
print(my_list[:-5])

# elements 6th to end
print(my_list[5:])

# elements beginning to end
print(my_list[:])

Output

['r', 'l', 'd']
['w', 'o', 'r','l']
['i', 't', 'e','c']
['w', 'o', 'r', 'l', 'd', 'o', 'f', 'i', 't', 'e', 'c','h']

How to change or add elements to a list?

Lists are mutable, meaning their elements can be changed, unlike string or tuple.

We can use the assignment operator (=) to change an item or a range of items.

# Correcting mistake values in a list
odd = [2, 4, 6, 8]

# change the 1st item    
odd[0] = 1            

print(odd)

# change 2nd to 4th items
odd[1:4] = [3, 5, 7]  

print(odd)                   

Output

[1, 4, 6, 8]
[1, 3, 5, 7]

We can add one item to a list using the append() the method or add several items using extend() method.

# Appending and Extending lists in Python
odd = [1, 3, 5]

odd.append(7)

print(odd)

odd.extend([9, 11, 13])

print(odd)

Output

[1, 3, 5, 7]
[1, 3, 5, 7, 9, 11, 13]

We can also use + the operator to combine two lists. This is also called concatenation.

The * the operator repeats a list for the given number of times.

# Concatenating and repeating lists
odd = [1, 3, 5]

print(odd + [9, 7, 5])

print(["re"] * 3)

Output

[1, 3, 5, 9, 7, 5]i
['re', 're', 're']

Moreover, we can insert one item at a desired location by using the method insert() or supplement various things by pressing it into an empty slice of a list.

# Demonstration of list insert() method
odd = [1, 9]
odd.insert(1,3)

print(odd)

odd[2:2] = [5, 7]

print(odd)

Output

[1, 3, 9]
[1, 3, 5, 7, 9]

How to delete or remove elements from a list?

We can delete one or more items from a list using the keyword del. It can even delete the list entirely.

# Deleting list items
my_list = ['p', 'r', 'o', 'b', 'l', 'e', 'm']

# delete one item
del my_list[2]

print(my_list)

# delete multiple items
del my_list[1:5]

print(my_list)

# delete entire list
del my_list

# Error: List not defined
print(my_list)

Output

['p', 'r', 'b', 'l', 'e', 'm']
['p', 'm']
Traceback (most recent call last):
  File "<string>", line 18, in <module>
NameError: name 'my_list' is not defined

We can use remove() method to expel the given thing or pop() method to expel a thing at the given list.

The pop() technique evacuates and restores the last thing if the file isn’t given. This causes us to actualize records as stacks (first in, last out information structure).

We can also use the clear() method to empty a list.

my_list = ['p','r','o','b','l','e','m']
my_list.remove('p')

# Output: ['r', 'o', 'b', 'l', 'e', 'm']
print(my_list)

# Output: 'o'
print(my_list.pop(1))

# Output: ['r', 'b', 'l', 'e', 'm']
print(my_list)

# Output: 'm'
print(my_list.pop())

# Output: ['r', 'b', 'l', 'e']
print(my_list)

my_list.clear()

# Output: []
print(my_list)

['r', 'o', 'b', 'l', 'e', 'm']
o
['r', 'b', 'l', 'e', 'm']
m
['r', 'b', 'l', 'e']
[]

>>> my_list = ['p','r','o','b','l','e','m']
>>> my_list[2:3] = []
>>> my_list
['p', 'r', 'b', 'l', 'e', 'm']
>>> my_list[2:5] = []
>>> my_list
['p', 'r', 'm']

Some examples of Python list methods:

# Python list methods
my_list = [3, 8, 1, 6, 0, 8, 4]

# Output: 1
print(my_list.index(8))

# Output: 2
print(my_list.count(8))

my_list.sort()

# Output: [0, 1, 3, 4, 6, 8, 8]
print(my_list)

my_list.reverse()

# Output: [8, 8, 6, 4, 3, 1, 0]
print(my_list)

Output

1
2
[0, 1, 3, 4, 6, 8, 8]
[8, 8, 6, 4, 3, 1, 0]

List Comprehension: Elegant way to create new List

List comprehension is a rich and brief approach to make another rundown from a current rundown in Python.

A list comprehension comprises of an articulation followed by for statement inside square sections.

Here is an example to make a list with each item being increasing power of 2.

pow2 = [2 ** x for x in range(10)]
print(pow2)

Output

[1, 2, 4, 8, 16, 32, 64, 128, 256, 512]

This code is equivalent to:

pow2 = []
for x in range(10):
   pow2.append(2 ** x)

A list of comprehension can optionally contain more for or if statements. An optional if statement can filter out items for the new list. Here are some examples.

>>> pow2 = [2 ** x for x in range(10) if x > 5]
>>> pow2
[64, 128, 256, 512]
>>> odd = [x for x in range(20) if x % 2 == 1]
>>> odd
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
>>> [x+y for x in ['Python ','C '] for y in ['Language','Programming']]
['Python Language', 'Python Programming', 'C Language', 'C Programming']

Other List Operations in Python

List Membership Test

We can test if an item exists in a list or not, using the keyword in.

my_list = ['p', 'r', 'o', 'b', 'l', 'e', 'm']

# Output: True
print('p' in my_list)

# Output: False
print('a' in my_list)

# Output: True
print('c' not in my_list)

Output

True
False
True

Iterating Through a List

Using a for loop we can iterate through each item in a list.

for fruit in ['apple','banana','mango']:
    print("I like",fruit)

Output

I like apple
I like banana
I like mango

Please feel free to give your comment if you face any difficulty here.

For More Latest Articles Click on Below Link.

worldofitech