Python - Lists

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 psts and tuples, which we would see in this tutorial.

There are certain things you can do with all sequence types. These operations include indexing, spcing, 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 pst is a most versatile datatype available in Python which can be written as a pst of comma-separated values (items) between square brackets. Important thing about a pst is that items in a pst need not be of the same type.

Creating a pst is as simple as putting different comma-separated values between square brackets. For example −

pst1 = [ physics ,  chemistry , 1997, 2000];
pst2 = [1, 2, 3, 4, 5 ];
pst3 = ["a", "b", "c", "d"]

Similar to string indices, pst indices start at 0, and psts can be spced, concatenated and so on.

Accessing Values in Lists

To access values in psts, use the square brackets for spcing along with the index or indices to obtain value available at that index. For example −

#!/usr/bin/python

pst1 = [ physics ,  chemistry , 1997, 2000];
pst2 = [1, 2, 3, 4, 5, 6, 7 ];
print "pst1[0]: ", pst1[0]
print "pst2[1:5]: ", pst2[1:5]

pst1[0]:  physics
pst2[1:5]:  [2, 3, 4, 5]

#!/usr/bin/python

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

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

#!/usr/bin/python

pst1 = [ physics ,  chemistry , 1997, 2000];
print pst1
del pst1[2];
print "After deleting value at index 2 : "
print pst1

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

L = [ spam ,  Spam ,  SPAM! ]