Python – Lists

Python - Lists
Python - Lists

Python – Lists, The most primary facts shape in Python is the sequence. Each detail of a sequence is assigned a number of – its function or index. The first index is 0, the second one index is one, and so forth.

Python has six integrated forms of sequences, but the most common ones are lists and tuples, which we would see on this academic.

There are certain things you can do with all series sorts. These operations consist of indexing, slicing, including, multiplying, and checking for club. In addition, Python has built-in capabilities for finding the duration of a chain and for finding its biggest and smallest elements.

Python Lists

The list is a most flexible datatype available in Python which may be written as a listing of comma-separated values (objects) among rectangular brackets. Important component approximately a list is that gadgets in a list need not be of the identical kind.

Creating a listing is as easy as placing specific comma-separated values among rectangular brackets. For instance −

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

Similar to string indices, listing indices begin at zero, and lists may be sliced, concatenated and so on.

Accessing Values in Lists

To get admission to values in lists, use the square brackets for slicing in conjunction with the index or indices to reap fee available at that index. For instance −

#!/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 produces the following result −

list1[0]:  physics
list2[1:5]:  [2, 3, 4, 5]

Updating Lists

You can replace unmarried or multiple elements of lists by means of giving the slice at the left-hand aspect of the project operator, and you may upload to elements in a listing with the append() approach. For example −

#!/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 segment.

When the above code is finished, it produces the following result −

Value available at index 2 :
1997
New value available at index 2 :
2001

Delete List Elements

To eliminate a listing detail, you could use both the del statement in case you recognise precisely which detail(s) you are deleting or the get rid of() approach if you do now not realize. For instance −

#!/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.

Python – Lists, Basic List Operations

Lists respond to the + and * operators similar to strings; they suggest concatenation and repetition here too, except that the result is a brand new list, now not a string.

In fact, lists respond to all of the overall sequence operations we used on strings inside the previous chapter.

Python ExpressionResultsDescription
len([1, 2, 3])3Length
[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]TrueMembership
for x in [1, 2, 3]: print x,1 2 3Iteration

Python – Lists, Indexing, Slicing, and Matrixes

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

Assuming following enter −

L = ['spam', 'Spam', 'SPAM!']
Python ExpressionResultsDescription
L[2]SPAM!Offsets start at zero
L[-2]SpamNegative: count from the right
L[1:][‘Spam’, ‘SPAM!’]Slicing fetches sections

Python – Lists, Built-in List Functions & Methods

Python includes the following list functions −

Sr.No.Function with Description
1cmp(list1, list2)Compares elements of both lists.
2len(list)Gives the total length of the list.
3max(list)Returns item from the list with max value.
4min(list)Returns item from the list with min value.
5list(seq)Converts a tuple into list.

Python includes following list methods

Sr.No.Methods with Description
1list.append(obj)Appends object obj to list
2list.count(obj)Returns count of how many times obj occurs in list
3list.extend(seq)Appends the contents of seq to list
4list.index(obj)Returns the lowest index in list that obj appears
5list.insert(index, obj)Inserts object obj into list at offset index
6list.pop(obj=list[-1])Removes and returns last object or obj from list
7list.remove(obj)Removes object obj from list
8list.reverse()Reverses objects of list in place
9list.sort([func])Sorts objects of list, use compare func if given