Python list manipulation basics in detail.pdf

List Manipulation
based on CBSE curriculum
Class 11
By-
Neha Tyagi
PGT CS
KV 5 Jaipur II Shift, Jaipur Region
Neha Tyagi, KV 5 Jaipur II Shift

Introduction
• In Python, a list is a kind of container that contains collection
of any kind of values.
• A List is a mutable data type which means any value from the
list can be changed. For changed values , Python does not
create a new list.
• List is a sequence like a string and a tuple except that list is
mutable whereas string and tuple are immutable.
• In this chapter we will see the manipulation on lists. We will
see creation of list and various operation on lists via built in
functions.

List Creation
• List is a standard data type of Python. It is a sequence which
can store values of any kind.
• List is represented by square brackets “ [ ] “
For ex -
• [ ] Empty list
• [1, 2, 3] integers list
• [1, 2.5, 5.6, 9] numbers list (integer and float)
• [ ‘a’, ‘b’, ‘c’] characters list
• [‘a’, 1, ‘b’, 3.5, ‘zero’] mixed values list
• [‘one’, ’two’, ’three’] string list
• In Python, only list and dictionary are mutable data types, rest
of all the data types are immutable data types.

Creation of List
• List can be created in following ways-
• Empty list -
L = [ ]
• list can also be created with the following statement-
L = list( )
• Long lists-
even = [0, 2, 4, 6, 8, 10 ,12 ,14 ,16 ,18 ,20 ]
• Nested list -
L = [ 3, 4, [ 5, 6 ], 7]
This is tuple
Another method

Creation of List
-As we have seen in the example
That when we have supplied
values as numbers to a list even then
They have automatically converted to string
– If we want to pass values to a list in numeric form then we have to write
following function -
eval(input())
L=eval(input(“Enter list to be added “))
eval ( ) function identifies type of the passed string and then return it.
String Values
Another example

Accessing a List
• First we will see the similarities between a List and a String.
• List is a sequence like a string.
• List also has index of each of its element.
• Like string, list also has 2 index, one for forward indexing (from
0, 1, 2, 3, ….to n-1) and one for backward indexing(from -n to -
1).
• In a list, values can be accessed like string.
0 1 2 3 4 5 6 7 8 9 10 11 12 13
R E S P O N S I B I L I T Y
-14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1
Forward index
List
Backward index

Accessing a List
• len( ) function is used to get the length of a list.
• L[ i ] will return the values exists at i index.
• L [ i : j ] will return a new list with the values from i index to j index excluding
j index.
Important 1:membership
operator (in, not in) works
in list similarly as they work
in other sequence.
Important 2: + operator
adds a list at the end of
other list whereas *
operator repeats a list.

Difference between a List and a String
• Main difference between a List and a string is that string is
immutable whereas list is mutable.
• Individual values in string can’t be change whereas it is
possible with list.
Value didn’t
change in string.
Error shown. Value got changed
in list specifying
list is mutable

Traversal of a list
• Traversal of a list means to access and process each and
every element of that list.
• Traversal of a list is very simple with for loop –
for <item> in <list>:
*Python supports UNICODE therefore
output in Hindi is also possible

Comparison of Lists
• Relational operators are used to compare two different lists.
• Python compares lists or tuples in lexicographical order,
means comparing sequences should be of same type and
their elements should also be of similar type.
• In first example, python did not
raise the error because both the
lists are same.
• In second comparison, both the
lists are not similar hence, python
raised the error.
Some
examples

List Operations (+, *)
• Main operations that can be performed on lists are joining list,
replicating list and list slicing.
• To join Lists,+ operator , is used which joins a list at the end of
other list. With + operator, both the operands should be of list
type otherwise error will be generated.
• To replicate a list, * operator , is used.

List Slicing
• To slice a List, syntax is seq = list [ start : stop ]
• Another syntax for List slicing is –
seq=list[start:stop:step]

Use of slicing for list Modification
• Look carefully at following examples-
Here also, new value is being assigned.
New value is being assigned here.
See the difference between both the results.
144 is a value and not a sequence.

List Manipulation
• Element Appending in List list.append(item)
• Updating List elements list[index]=<new value>
• Deletion of List elements del list[index]
Important: if we write del list complete
list will be deleted.
Important: del
command can be
used to delete an
element of the list
or a complete slice
or a complete list.

List Manipulation
• Only one element will be deleted on pop() from list.
• pop ( ) function can not delete a slice.
• pop ( ) function also returns the value being deleted.
list.pop(<index>)
1st item
Last item
6th item

List Functions and Methods
– Python provides some built-in functions for list manipulation
– Syntax is like <list-object>.<method-name>
Function Details
List.index(<item>) Returns the index of passed items.
List.append(<item>) Adds the passed item at the end of list.
List.extend(<list>) Append the list (passed in the form of argument) at the end of list
with which function is called.
List.insert(<pos>,<item>) Insert the passed element at the passed position.
List.pop(<index>) Delete and return the element of passed index. Index passing is
optional, if not passed, element from last will be deleted.
List.remove(<value>) It will delete the first occurrence of passed value but does not
return the deleted value.

Function Details
List.clear ( ) It will delete all values of list and gives an empty list.
List.count (<item>) It will count and return number of occurrences of the passed element.
List.reverse ( ) It will reverse the list and it does not create a new list.
List.sort ( ) It will sort the list in ascending order. To sort the list in descending
order, we need to write----- list.sort(reverse =True).

• List.index ( ) function:
• List.append( ) function:
• List.extend( ) function:
• List.insert( ) function:

• List.pop ( ) function:
• List.remove( ) function:
• List.count( ) function:

• List.reverse( ) function:
• List.sort( ) function:
Important
• To sort a list in reverse order, write in following manner–
List.sort(reverse=True)
• If a list contains a complex number, sort will not work.

Thank you
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Python list manipulation basics in detail.pdf

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