CLASS -11 COMPUTER SCIENCE
CHAPTER- 7 LIST MANIPULATION
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NOTES FOR COMPLETE UNDERSTANDING -
- A list is like a container that stores collection
of any kind of values.
- A List is a mutable data type i.e. any value from the
list can be updated later if wanted. For updated values , Python does not
create a new list.
- List is a series like a string and a tuple except of the fact that list is
mutable whereas string and tuple are immutable.
- List Creation :
- List is a standard data type of Python. It is a sequence/series which
can store values of any variety.
- List is represented by square brackets “ [ ] “ For eg. - • [ ] <---- 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 and other 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 - • list1 = list( )
- If we want to pass values to a list in numeric form then we have to write
following function : -L=eval(input(“Enter list to be added “)) *eval ( ) function identifies type of the passed string and then return it.
- Accessing a List :
- List is a sequence like a string.
- List also have index of each of its element. List also has 2 type of index :
- forward indexing (from
0, 1, 2, 3, 4, 5, 6, .......to L-1 )
- backward indexing (from -L to -
1).
- In a list, values can be accessed like string.
- 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. *NOTE : membership
operator (in, not in) works
in list alike they work
in strings. *NOTE : + operator
adds a list at the end of
other list whereas *
operator repeats a list.
- Difference between a List and a String :
- A string is
immutable whereas list is mutable.
- Individual values in string can’t be change whereas it is
possible with list
- Traversal of a list :
- It means to access each and
every element of that list.
- It is done with for loop.
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
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]
Element Appending in List list.append(item)
Updating List elements list[index]=new value
- Deletion of List elements del list[index] *NOTE :if we write del list complete
list will be deleted. *NOTE : del
command can be
used to delete an
element of the list
or a complete slice
or a complete list.
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.
*NOTE : 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.
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