List is
group of values in between square brackets separated by commas.
>>> primes=[2, 3, 5, 7, 11, 13, 17, 19, 23] >>> primes [2, 3, 5, 7, 11, 13, 17, 19, 23]
‘primes’ is
a list that contain prime numbers.
>>> students=["Hari", "Krishna", "Kiran", "Ravi"] >>> students ['Hari', 'Krishna', 'Kiran', 'Ravi']
‘students’
is a list that contain all student names.
List can
contain any type of data.
>>> objects=[1, 3, "Hello", 10.23] >>> objects [1, 3, 'Hello', 10.23]
You can
access elements of list by using index.
>>> objects [1, 3, 'Hello', 10.23] >>> objects[0] 1 >>> objects[2] 'Hello'
objects[0]
return the first element of list objects.
objects[1]
return the second element of list objects.
>>> objects [1, 3, 'Hello', 10.23] >>> objects[-1] 10.23 >>> objects[-3] 3
Slicing
Slicing is
used to get sub list.
Example
|
Description
|
list[start:end]
|
Returns
sub list from index start (included) to end index (excluded).
|
list[:end]
|
Returns
sub list from index 0(included) to end index (excluded).
|
list[start:]
|
Return sub
list from index start to till end.
|
list[-2:]
|
Return
list from 2nd last to end.
|
>>> objects [1, 3, 'Hello', 10.23] >>> objects[-1] 10.23 >>> objects[-3] 3 >>> objects [1, 3, 'Hello', 10.23] >>> >>> objects[:] [1, 3, 'Hello', 10.23] >>> >>> objects[2:] ['Hello', 10.23] >>> >>> objects[:3] [1, 3, 'Hello'] >>> >>> objects[-2:] ['Hello', 10.23]
Concatenate two lists
'+' Operator
is used to concatenate two lists.
>>> even=[2, 4, 6, 8, 10] >>> odd=[1, 3, 5, 7, 9] >>> numbers = even+odd >>> numbers [2, 4, 6, 8, 10, 1, 3, 5, 7, 9]
Lists are mutable; you can change the values of list.
>>> numbers [2, 4, 6, 8, 10, 1, 3, 5, 7, 9] >>> numbers[0]=12 >>> numbers[1]=14 >>> numbers [12, 14, 6, 8, 10, 1, 3, 5, 7, 9]
Add elements to end of list
List provides ‘append’ method to add new
elements to the end of a list.
>>> numbers [12, 14, 6, 8, 10, 1, 3, 5, 7, 9] >>> >>> numbers.append(11) >>> numbers.append(13) >>> >>> numbers [12, 14, 6, 8, 10, 1, 3, 5, 7, 9, 11, 13]
Assignment to slices
If you want
to replace sequence of elements in a list, you can use slice notation.
numbers[2:5]
= [21, 22, 23]
Above
statement replace elements at index 2, 3, 4 with 21, 22, 23 respectively.
numbers[:] =
[]
Above statement clear the list by replacing all
the elements with an empty list.
>>> numbers [12, 14, 6, 8, 10, 1, 3, 5, 7, 9, 11, 13] >>> >>> numbers[2:5]=[21, 22, 23] >>> numbers [12, 14, 21, 22, 23, 1, 3, 5, 7, 9, 11, 13] >>> >>> numbers[:] = [] >>> numbers []
Get length of the list
By using
‘len’ function, you can get the length of the list.
>>> vowels=['a', 'e', 'i', 'o', 'u'] >>> len(vowels) 5
Nested
lists
A list can be nested in other list. For
example, in below example, numbers contains 3 lists, first list represent odd
numbers, second list represent even numbers and third list represent prime
numbers.
>>> numbers=[[1, 3, 5, 7],[2, 4, 6, 8],[2, 3, 5, 7, 11]] >>> numbers [[1, 3, 5, 7], [2, 4, 6, 8], [2, 3, 5, 7, 11]] >>> >>> numbers[0] [1, 3, 5, 7] >>> >>> numbers[1] [2, 4, 6, 8] >>> >>> numbers[2] [2, 3, 5, 7, 11] >>> >>> >>> len(numbers) 3 >>> len(numbers[0]) 4 >>> len(numbers[1]) 4 >>> len(numbers[2]) 5 >>> >>> numbers[0][1]=9 >>> numbers[1][1:4] = [10, 12, 14] >>> numbers [[1, 9, 5, 7], [2, 10, 12, 14], [2, 3, 5, 7, 11]]
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