List concepts in python part 1

What is List

• A List can store the sequence of various types of data.
• A list is a container data type.Container is a an entity which contains multiple data items.It is also known as a collection.
• There are some container data types in python.

1. List
2. Tuple
3. Set
4. Dictionary

• Container data type are also known as compound data types.
• Lists are mutable in python.It means we can change the list element after it created.
• A list can be collection of Items with different data types(int,string,float etc.).
• A list can contain similar and dissimilar both data types.
• The items in the list are separated with comma(,) and enclosed with the square brackets [].

e.g.

Dissimilar items:-It contains collection of different data types.

list1=['ram',20,10.89,'cow','tiger']

Similar items:-It contains collection of same data types.

list2=[1,2,3,4,5,6,7,,8,9,10]

list1=['ram',20,10.89,'cow','tiger']
list2=[1,2,3,4,5,6,7,8,9,10]
print(type(list1))
print(type(list2))

Output:-

<class 'list'>

<class 'list'>

Properties of List:-There are some properties of list as given below.

• Lists are mutable (changeable).
• The Items in a list can be repeated.Means a list may contain duplicate items.
• The lists are ordered.
• The items in the list can be access by index.
• A list contains similar and dissimilar  both data type items.
• A list always uses a square brackets [] and each item in list separated by comma(,).

e.g.

list1=['ram',20,10.89,'cow','tiger']
list2=['ram',20,10.89,'tiger','cow']
list3=['ram',20,10.89,'tiger','cow']
print(list1==list2)
print(list2==list3)

Output:-

False

True

Descriptions:-

• list1 and list2 have same elements but index value of items their items are changed.Therefore list1 and list2 are not equal.
• list2 and list3 are ordered list because both list of items have same index value.Therefore  list2 and list3 are equal.

Accessing List Elements:-

• A list item can be accessed using index value like string.Hence it is known as sequence types.
• A list index value start from zero like string.

e.g.

list=[10,20,30,40,50,60,70,80]

Now access the list value:-

list[0]=10

list[1]=20

list[2]=30

list[3]=40

list[4]=50

list[5]=60

list[6]=70

list[7]=80

• A list can be sliced like string.

e.g.

Syntax:-

list(start:stop:step)

start:-It denotes the starting index value of the list.

stop:- It denotes the last index value of the list.

step:- It denotes the increment value of the ordered list.

Access the element in forward direction:-

vowel=['a','e','i','o','u']
print(vowel[0])
print(vowel[1])
print(vowel[2])
print(vowel[3])
print(vowel[4])
#slice the elements
print("slice element values:")
print(vowel[:])
print(vowel[1:4])
print(vowel[1:])
print(vowel[1:4:1])
print(vowel[:4])

Output:-

a

e

i

o

u

slice element values:

['a', 'e', 'i', 'o', 'u']

['e', 'i', 'o']

['e', 'i', 'o', 'u']

['e', 'i', 'o']

['a', 'e', 'i', 'o']

>>> 

Access the element in backward direction:-

vowel=['a','e','i','o','u']
print(vowel[-1])
print(vowel[-2])
print(vowel[-3])
print(vowel[-4])
print(vowel[-5])
#slice the elements
print("slice element values:")
print(vowel[:])
print(vowel[:-1])
print(vowel[-3:-1])
print(vowel[-3:])
print(vowel[-1:-4:-2])
print(vowel[:-5])

Output:-

u

o

i

e

a

slice element values:

['a', 'e', 'i', 'o', 'u']

['a', 'e', 'i', 'o']

['i', 'o']

['i', 'o', 'u']

['u', 'i']

[]

• We can print entire list by using the name of any list.

e.g.

animals=['Lion','Tiger','Horse','Cow']
print(animals)

Output:-

['Lion', 'Tiger', 'Horse', 'Cow']

• A list of all keywords in python is also obtained as a list.

import keyword
print(keyword.kwlist)

Output:-

['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']

Updating the List values:-

• We know ,lists are mutable(changeable) but strings are immutable (unchangeable).
• We can update the values in the list by using assignment and slice operator in python.
• Python also provides some methods like append() and insert() which can be used to insert value to the list.
• The list elements can also be deleted by using del keyword.Python provides remove() method if we don't know which element is to be deleted from the list.

e.g.

numbers=[1,2,3,4,5,6,7,8,9,10]
print(numbers)
#update the value of 3rd index in the list
numbers[3]=40
print(numbers)
#Add/update multiple values in the list
numbers[4:8]=[50,60,70,80]
print(numbers)
#Add the value at the end of the list by two method
numbers[9]=[100]
#numbers[-1]=[100]
print(numbers)

Output:-

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

[1, 2, 3, 40, 5, 6, 7, 8, 9, 10]

[1, 2, 3, 40, 50, 60, 70, 80, 9, 10]

[1, 2, 3, 40, 50, 60, 70, 80, 9, [100]]

>>> 

program 1: Write a python program to add items in empty list by user.

#Declaring empty list
lst=[]
num=int(input("Enter the number of element in the list:\n"))
for i in range(0,num):
    lst.append(input("Enter the Value:\n"))
#print the list items
str=input("Do you want to print list values press: yes/no \n")
if(str=='yes'):
    for j in lst:
        print(j,end=" ")
elif(str=='no'):
    print("Sorry!I am unable to print list values...")
else:
    print("Please enter valid data...")

Output:-

Enter the number of element in the list:

5

Enter the Value:

1

Enter the Value:

56

Enter the Value:

78

Enter the Value:

90

Enter the Value:

55

Do you want to print list values press: yes/no 

yes

1 56 78 90 55 

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