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Python 3 - Lists
Rajesh Mehta
a year ago
Table of Contents
- Introduction
- Python Lists
- Accessing Values in Lists
- Updating Lists
- Delete List Elements
- Basic List Operations
1. Indexing, Slicing, and Matrixes
- Built-in List Functions and Methods
Introduction
The most basic data structure in Python is the sequence. Each element of a sequence is assigned a number - its position or index. The first index is zero, the second index is one, and so forth.
Python has six built-in types of sequences, but the most common ones are lists and tuples, which we would see in this tutorial.
There are certain things you can do with all the sequence types. These operations include indexing, slicing, adding, multiplying, and checking for membership. In addition, Python has built-in functions for finding the length of a sequence and for finding its largest and smallest elements.
Python Lists
The list is the most versatile datatype available in Python, which can be written as a list of comma-separated values (items) between square brackets. The important thing about a list is that the items in a list need not be of the same type.
Creating a list is as simple as putting different comma-separated values between square brackets. For example
list1 = ['physics', 'chemistry', 1997, 2000];
list2 = [1, 2, 3, 4, 5 ];
list3 = ["a", "b", "c", "d"];Similar to string indices, list indices start at 0, and lists can be sliced, concatenated and so on.
Accessing Values in Lists
To access values in lists, use the square brackets for slicing along with the index or indices to obtain value available at that index. For example −
#!/usr/bin/python3
list1 = ['physics', 'chemistry', 1997, 2000]
list2 = [1, 2, 3, 4, 5, 6, 7 ]
print ("list1[0]: ", list1[0])
print ("list2[1:5]: ", list2[1:5])When the above code is executed, it produces the following result −
list1[0]: physics
list2[1:5]: [2, 3, 4, 5]Updating Lists
You can update single or multiple elements of lists by giving the slice on the left-hand side of the assignment operator, and you can add to elements in a list with the append() method. For example −
#!/usr/bin/python3
list = ['physics', 'chemistry', 1997, 2000]
print ("Value available at index 2 : ", list[2])
list[2] = 2001
print ("New value available at index 2 : ", list[2])
Note − The append() method is discussed in the subsequent section.
When the above code is executed, it produces the following result −
Value available at index 2 : 1997
New value available at index 2 : 2001Delete List Elements
To remove a list element, you can use either the del statement if you know exactly which element(s) you are deleting. You can use the remove() method if you do not know exactly which items to delete. For example −
#!/usr/bin/python3
list = ['physics', 'chemistry', 1997, 2000]
print (list)
del list[2]
print ("After deleting value at index 2 : ", list)When the above code is executed, it produces the following result −
['physics', 'chemistry', 1997, 2000]
After deleting value at index 2 : ['physics', 'chemistry', 2000]Note − remove() method is discussed in the subsequent section.
Basic List Operations
Lists respond to the &plus and * operators much like strings; they mean concatenation and repetition here too, except that the result is a new list, not a string.
In fact, lists respond to all of the general sequence operations we used on strings in the prior chapter.
1. Indexing, Slicing, and Matrixes
Since lists are sequences, indexing and slicing work the same way for lists as they do for strings.
Assuming the following input −
L = ['C++'', 'Java', 'Python']Built-in List Functions and Methods
Python includes the following list functions −
Python includes the following list methods −
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