Python List
Python list is a data structure which is used to store various
types of data.
In Python, lists are mutable i.e., Python will not create a new
list if we modify an element of the list.
It works as a container that holds other objects in a given order.
We can perform various operations like insertion and deletion on list.
A list can be composed by storing a sequence of different type of
values separated by commas.
Python list is enclosed between square([]) brackets and elements
are stored in the index basis with starting index 0.
Python
List Example
data1=[1,2,3,4];
data2=['x','y','z'];
data3=[12.5,11.6];
data4=['raman','rahul'];
data5=[];
data6=['abhinav',10,56.4,'a'];
A list can be created by putting the value inside the square bracket
and separated by comma.
Python
List Syntax
<list_name>=[value1,value2,value3,...,valuen];
Syntax
to Access Python List
<list_name>[index]
Python allows us to access value from the list by various ways.
Python Accessing List Elements Example
data1=[1,2,3,4];
data2=['x','y','z'];
print data1[0]
print data1[0:2]
print data2[-3:-1]
print data1[0:]
print data2[:2]
Output:
>>>
>>>
1
[1, 2]
['x', 'y']
[1, 2, 3, 4]
['x', 'y']
>>>
Elements
in a Lists:
Following
are the pictorial representation of a list. We can see that it allows to access
elements from both end (forward and backward).
Data=[1,2,3,4,5];
Data[0]=1=Data[-5] , Data[1]=2=Data[-4] , Data[2]=3=Data[-3] ,
Data[3]=4=Data[-2] , Data[4]=5=Data[-1].
Python List Operations
Apart from creating and accessing elements from the list, Python
allows us to perform various other operations on the list. Some common
operations are given below
a)
Adding Python Lists
In Python, lists can be added by using the concatenation operator(+)
to join two lists.
Add
lists Example 1
list1=[10,20]
list2=[30,40]
list3=list1+list2
print list3
Output: >>>
[10, 20, 30, 40]
>>>
Add
lists Example 2
list1=[10,20]
list1+30
print list1
Output:
Traceback (most recent call last):
File "C:/Python27/lis.py", line 2, in <module>
list1+30
b)
Python Replicating lists
Replicating means repeating, It can be performed by using '*'
operator by a specific number of time.
Python
list Replication Example
list1=[10,20]
print list1*1
Output:
>>>
[10, 20]
>>>
c)Python
List Slicing
A subpart of a list can be retrieved on the basis of index. This
subpart is known as list slice. This feature allows us to get sub-list of specified
start and end index.
Python List Slicing Example
list1=[1,2,4,5,7]
print list1[0:2]
print list1[4]
list1[1]=9
print list1
Output:
>>>
[1, 2]
7
[1, 9, 4, 5, 7]
>>>
Python
List Other Operations
Apart from above operations various other functions can also be
performed on List such as Updating, Appending and Deleting elements from a
List.
Python
Updating List
To update or change the value of particular index of a list,
assign the value to that particular index of the List.
Python Updating List Example
data1=[5,10,15,20,25]
print "Values of list are: "
print data1
data1[2]="Multiple of 5"
print "Values of list are: "
print data1
Output:
>>>
Values of list are:
[5, 10, 15, 20, 25]
Values of list are:
[5, 10, 'Multiple of 5', 20, 25]
>>>
Appending
Python List
Python provides, append() method which is used to append i.e., add
an element at the end of the existing elements.
Python Append List Example
list1=[10,"rahul",'z']
print "Elements of List are: "
print list1
list1.append(10.45)
print "List after appending: "
print list1
Output:
>>>
Elements of List are:
[10, 'rahul', 'z']
List after appending:
[10, 'rahul', 'z', 10.45]
>>>
Deleting
Elements
In Python, del statement can be used to delete an element from the list. It
can also be used to delete all items from startIndex to endIndex.
Python delete List Example
list1=[10,'rahul',50.8,'a',20,30]
print list1
del list1[0]
print list1
del list1[0:3]
print list1
Output:
>>>
[10, 'rahul', 50.8, 'a', 20, 30]
['rahul', 50.8, 'a', 20, 30]
[20, 30]
>>>
Python
lists Method
Python provides various Built-in functions and methods for Lists
that we can apply on the list.
Following are the common list functions.
|
Function
|
Description
|
|
min(list)
|
It
returns the minimum value from the list given.
|
|
max(list)
|
It
returns the largest value from the given list.
|
|
len(list)
|
It
returns number of elements in a list.
|
|
cmp(list1,list2)
|
It
compares the two list.
|
|
list(sequence)
|
It
takes sequence types and converts them to lists.
|
Python List min() method Example
This method is used to get min value from the list.
list1=[101,981,'abcd','xyz','m']
list2=['aman','shekhar',100.45,98.2]
print "Minimum value in List1: ",min(list1)
print "Minimum value in List2: ",min(list2)
Output:
>>>
Minimum value in List1: 101
Minimum value in List2: 98.2
>>>
Python List max() method Example
This method is used to get max value from the list.
list1=[101,981,'abcd','xyz','m']
list2=['aman','shekhar',100.45,98.2]
print "Maximum value in List : ",max(list1)
print "Maximum value in List : ",max(list2)
Output:
>>>
Maximum value in List : xyz
Maximum value in List : shekhar
>>>
Python List len() method Example
This method is used to get length of the the list.
list1=[101,981,'abcd','xyz','m']
list2=['aman','shekhar',100.45,98.2]
print "No. of elements in List1: ",len(list1)
print "No. of elements in List2: ",len(list2)
Output:
>>>
No. of elements in List1 : 5
No. of elements in List2 : 4
>>>
Python List cmp() method Example
Explanation: If elements are of the same type, perform the
comparison and return the result. If elements are different types, check whether
they are numbers.
- If
numbers, perform comparison.
- If
either element is a number, then the other element is returned.
- Otherwise,
types are sorted alphabetically .
If we reached the end of one of the lists, the longer list is
"larger." If both list are same it returns 0.
Python List cmp() method Example
list1=[101,981,'abcd','xyz','m']
list2=['aman','shekhar',100.45,98.2]
list3=[101,981,'abcd','xyz','m']
print cmp(list1,list2)
print cmp(list2,list1)
print cmp(list3,list1)
Output:
>>>
-1
1
0
>>>
Python List list(sequence) method Example
This method is used to form a list from the given sequence of
elements.
1.
seq=(145,"abcd",'a')
data=list(seq)
print "List formed is : ",data
Output:
>>>
List formed is : [145, 'abcd', 'a']
>>>
There are following built-in methods of List
|
Methods
|
Description
|
|
index(object)
|
It
returns the index value of the object.
|
|
count(object)
|
It
returns the number of times an object is repeated in list.
|
|
pop()/pop(index)
|
It
returns the last object or the specified indexed object. It removes the
popped object.
|
|
insert(index,object)
|
It
inserts an object at the given index.
|
|
extend(sequence)
|
It adds
the sequence to existing list.
|
|
remove(object)
|
It
removes the object from the given List.
|
|
reverse()
|
It reverses
the position of all the elements of a list.
|
|
sort()
|
It is
used to sort the elements of the List.
|
Python List index() Method Example
data = [786,'abc','a',123.5]
print "Index of 123.5:", data.index(123.5)
print "Index of a is", data.index('a')
Output:
>>>
Index of 123.5 : 3
Index of a is 2
>>>
Python List count(object) Method Example
data = [786,'abc','a',123.5,786,'rahul','b',786]
print "Number of times 123.5 occured is", data.count(123.5)
print "Number of times 786 occured is", data.count(786)
Output:
>>>
Number of times 123.5 occured is 1
Number of times 786 occured is 3
>>>
Python List pop()/pop(int) Method Example
data = [786,'abc','a',123.5,786]
print "Last element is", data.pop()
print "2nd position element:", data.pop(1)
print data
Output:
>>>
Last element is 786
2nd position element:abc
[786, 'a', 123.5]
>>>
Python List insert(index,object) Method Example
data=['abc',123,10.5,'a']
data.insert(2,'hello')
print data
Output:
>>>
['abc', 123, 'hello', 10.5, 'a']
>>>
Python List extend(sequence) Method Example
data1=['abc',123,10.5,'a']
data2=['ram',541]
data1.extend(data2)
print data1
print data2
Output:
>>>
['abc', 123, 10.5, 'a', 'ram', 541]
['ram', 541]
>>>
Python List remove(object) Method Example
data1=['abc',123,10.5,'a','xyz']
data2=['ram',541]
print data1
data1.remove('xyz')
print data1
print data2
data2.remove('ram')
print data2
Output:
>>>
['abc', 123, 10.5, 'a', 'xyz']
['abc', 123, 10.5, 'a']
['ram', 541]
[541]
>>>
Python List reverse() Method Example
list1=[10,20,30,40,50]
list1.reverse()
print list1
Output:
>>>
[50, 40, 30, 20, 10]
>>>
Python List sort() Method Example
list1=[10,50,13,'rahul','aakash']
list1.sort()
print list1
Output:
>>>
[10, 13, 50, 'aakash', 'rahul']
>>>
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