Python List Basics
Python list is a sequence of objects in an ordered fashion. It is similar to arrays in other programming languages but it is heterogeneous in nature. A single list can hold different types of data objects(string, integer, float etc.). It can hold other lists also, a list inside another list is called a nested list.
Note: You can run examples in this article on trinket.io online.
Create an empty list
>>> list1 = []
>>> print list1
[] #output
Create a list with three elements
>>> list1 = [1, "hackinbits.com", 2.3]
Accessing a list element
>>> list1 = [1, "hackinbits.com", 2.3]
>>> list1[1]
'hackinbits.com' #output
Updating a list
>>> list1 = [1, 2, 3, 4]
>>> list1[1] = 34
>>> print list1
[1, 34, 3, 4] #output
An empty list can also be created using list() method
>>> list1 = list()
>>> print list1
[] #output
There are various operations that can be performed on lists using in-build list methods.
append()
Add a new element to the end of the list.
>>> list1 = [1, 2]
>>> print list1
[1, 2] #output
>>> list1.append(3)
>>> list1.append(4)
>>> print list1
[1, 2, 3, 4] #output
insert()
Insert a new element at the specified index.
>>> list1 = [1, 2, 3]
>>> list1.insert(23, 1)
>>> print list1
[1, 23, 2, 3] #output
remove()
Deletes the specified element from the list.
>>> list1 = [1, 2, 3]
>>> list1.remove(2)
[1, 3] #output
pop()
Removes an item from the list and also returns it.
>>> list1 = [1, 2, 3]
>>> item = list1.pop()
>>> print list1
[1, 2] #output
>>> print item
3 #output
index()
Returns the index of an element that matches first.
>>> list1 = [1, 2, 3, 4]
>>> list1.index(3)
2 #output
count()
Returns the total number of item count, passed as an argument to the method.
>>> list1 = [1, 2, 3, 4, 5, 3]
>>> list1.count(3)
2 #output
reverse()
Inverts the order of the elements in a list.
>>> list1 = [1, 2, 3]
>>> list1.reverse()
[3, 2, 1] #output
extend()
Extends a list by adding elements from another list (passed as a parameter).
>>> list1 = [1, 2]
>>> list2 = [3, 4]
>>> list1.extend(list2)
>>> print list1
[1, 2, 3, 4] #output
>>> print list2
[3, 4] #output
sort()
Orders the elements of a list in an ascending manner.
>>> list1 = [5, 6,3, 90, 3, 2]
>>> list1.sort()
>>> print list1
[2, 3, 3, 5, 6, 90] #output
A list copy operation can be performed using the assignment operator.
>>> list1 = [1, 2, 3, 4]
>>> list2 = list1
>>> print list2
[1, 2, 3, 4] #output
This kind of copy using the assignment operator is called shallow copy. Any changes in list1 will make the same change in list2.
>>> list1[2] = 22
>>> print list2
[1, 2, 22, 4] #output
Solution to shallow copy in python list:
Using the in-built copy module
>>> import copy
>>> list1 = [1, 2, 3, 4]
>>> list2 = copy.deepcopy(list1)
>>> print list2
[1, 2, 3, 4] #output
>>> list1[1] = 22
>>> print list2
[1, 2, 3, 4] #output
Creating another list and copying the content
>>> list1 = [1, 2, 3, 4]
>>> list2 = []
>>> for i in list1: list2.append(i)
>>> list1[1] = 22
>>> print list2
[1, 2, 3, 4] #output
Originally published at hackinbits.com.
