Python Lists


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The least basic data design in Python is the sequence. Each component of a sequence is allotted a number - its place or index. The initial index is zero, the another index is one, and so off.

Python has six reinforced-in types of sequences, however the most joint ones are lists and tuples, which we would perceive in this tutorial.

There are definite things that users can opt with entire sequence types. These operations incorporates indexing, slicing, adding, multiplying, and verifying for membership. Additionally, Python has structured functions for discovering the length of a sequence and its largest and smallest elements.

Python Lists

The database is a most versatile datatype accessible in Python that can be written as a list of comma-separated values (items) between square brackets. Essential thing related a list is that items in a list require not be of the similar type.

Developing a list is as simple as putting various comma-separated values between square brackets. For instance :

list1 = ['physics', 'chemistry', 1997, 2000];
list2 = [1, 2, 3, 4, 5 ];
list3 = ["a", "b", "c", "d"]

Same to string indices, list indices start at 0, and lists can be sliced, concatenated and so on.

Accessing Values in Lists

To approach values in lists, use the square brackets for slicing along with the index or indices to acquire value accessible at that index. For example :

#!/usr/bin/python

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 supplies 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 delivering the slice on the left-hand side of the deployment operator, and you can add to elements in a list with the append() method. For instance :

#!/usr/bin/python

list = ['physics', 'chemistry', 1997, 2000];
print "Value available at index 2 : "
print list[2]
list[2] = 2001;
print "New value available at index 2 : "
print list[2]

Note − append() method is discussed in 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 :
2001

Delete List Elements

To remove a list element, you can use either the del statement if you know exactly which element(s) you are deleting or the remove() method if you do not know. For example :

#!/usr/bin/python

list1 = ['physics', 'chemistry', 1997, 2000];
print list1
del list1[2];
print "After deleting value at index 2 : "
print list1

When the above code is executed, it produces following result

['physics', 'chemistry', 1997, 2000]
After deleting value at index 2 :
['physics', 'chemistry', 2000]

Note − remove() method is discussed in subsequent section.

Basic List Operations

Lists respond to the + 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.

Python Expression

Results

Description

len([1, 2, 3])

3

Length

[1, 2, 3] + [4, 5, 6]

[1, 2, 3, 4, 5, 6]

Concatenation

['Hi!'] * 4

['Hi!', 'Hi!', 'Hi!', 'Hi!']

Repetition

3 in [1, 2, 3]

True

Membership

for x in [1, 2, 3]: print x,

1 2 3

Iteration

Indexing, Slicing, and Matrixes

Because lists are sequences, indexing and slicing work the same way for lists as they do for strings.

Assuming following input :

L = ['spam', 'Spam', 'SPAM!']

Python Expression

Results

Description

L[2]

SPAM!

Offsets start at zero

L[-2]

Spam

Negative: count from the right

L[1:]

['Spam', 'SPAM!']

Slicing fetches sections

Built-in List Functions & Methods

Python includes the following list functions −

Sr.No.

Function with Description

1

cmp(list1, list2)

Compares elements of both lists.

2

len(list)

Gives the total length of the list.

3

max(list)

Returns item from the list with max value.

4

min(list)

Returns item from the list with min value.

5

list(seq)

Converts a tuple into list.

Python includes following list methods

Sr.No.

Methods with Description

1

list.append(obj)

Appends object obj to list

2

list.count(obj)

Returns count of how many times obj occurs in list

3

list.extend(seq)

Appends the contents of seq to list

4

list.index(obj)

Returns the lowest index in list that obj appears

5

list.insert(index, obj)

Inserts object obj into list at offset index

6

list.pop(obj=list[-1])

Removes and returns last object or obj from list

7

list.remove(obj)

Removes object obj from list

8

list.reverse()

Reverses objects of list in place

9

list.sort([func])

Sorts objects of list, use compare func if given

Here at Intellinuts, we have created a complete Python tutorial for Beginners to get started in Python.



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