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

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])

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

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

Updating Lists

You can update single or multiple elements of psts by giving the spce on the left-hand side of the assignment operator, and you can add to elements in a pst with the append() method.

For example

#!/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])

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 pst 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

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

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 pke strings; they mean concatenation and repetition here too, except that the result is a new pst, not a string.

In fact, psts respond to all of the general sequence operations we used on strings in the prior chapter.