### Unit 1 - Lists, tuples and dictionary

CBSE Revision Notes

Class-11 Computer Science (New Syllabus)
Unit 1: Programming and Computational Thinking (PCT-1)

Lists, tuples and dictionary

In this section we’ll discuss lists, tuples and dictionary

Lists: Lists are the most versatile of Python's compound data types. A list contains items

separated by commas and enclosed within square brackets ([]). To some extent, lists are similar to arrays in C. One of the differences between them is that all the items belonging to a list can be of different data type. The values stored in a list can be accessed using the slice operator ([ ] and [:]) with indexes starting at 0 in the beginning of the list and working their way to end -1. The plus (+) sign is the list concatenation operator, and the asterisk (*) is the repetition operator. Let’s understand this with an example

list = [ 'abcd', 786 , 2.23, 'john', 70.2 ]

tinylist = [123, 'john']

print (list) # Prints complete list

print (list) # Prints first element of the list

print (list[1:3]) # Prints elements starting from 2nd till 3rd

print (list[2:]) # Prints elements starting from 3rd element

print (tinylist * 2) # Prints list two times

print (list + tinylist) # Prints concatenated lists

Maximum number from the list program: There are 2 ways to do this program

1. Using inbuilt function called max
2. Using loops

We will do this program from both ways

Using inbuilt function

list=[10,8,99,22,11,5] #initializing list

maximum=max(list) #it will return maximum number from the list

print("Maximum number from the list is",maximum)

Using loops:

list=[10,22,1,98,2,43,100]

maximum=list #putting the first value of list into variable maximum

for i in range(0, len(list)): #iterating through the list from 0 to total length of the list

if list[i]>maximum: #checking if next number is greater than the number saved

maximum=list[i] #if yes then put that value into maximum

print ("Largest number from the list is ",maximum) #print the value

Minimum number from the list: We’ll also do this program using both the methods

Using inbuilt function:

list=[10,8,99,22,11,5] #initializing list

minimum=min(list) #it will return minimum number from the list

print("minimum number from the list is",minimum)

Using loop:

list=[10,22,1,98,2,43,100]

minimum=list #putting the first value of list into variable minimum

for i in range(0, len(list)): #iterating through the list from 0 to total length of the list

if list[i]<minimum: #checking if next number is smaller than the number saved

minimum=list[i] #if yes then put that value into minimun

print ("Smallest number from the list is ",minimum) #print the value

Mean of numbers program:

list=[2,44,12,53,22]

sum=0

for i in range(0,len(list)):

sum=sum+list[i] #it will add all the items from the list

mean=sum/len(list) #to find the mean sum of items is divided by total number of items

print("Mean of numbers is ", mean)

Linear search:

list=[11,22,3,112,98,45,1]

print("Enter number you want to search")

num=eval(input()) #user enters the number he wants to search

flag=False

for i in range(0,len(list)): #iterates through the list

#checks every element with the number user entered if its equal it will print the message

if list[i]==num:

print("Number found")

flag=True #flag will set to true and will break the loop

break

if flag==False: #if flag is still false means number is not found

Tuples: Tuple is a sequence of immutable Python objects. Tuples are sequences, just like Lists. The main difference between the tuples and the lists is that the tuples cannot be changed unlike lists. Tuples use parentheses whereas lists use square brackets. let’s see how to create a tuple

tup1=("physics", "chemistry","biology",2012)

tup2=(1,2,3,4,5,6)

print ("tup1: ", tup1)

print ("tup2[1:5]: ", tup2[1:5])

when the above program will be executed it will give following result

tup1: 'physics'
tup2[1:5]: (2, 3, 4, 5)

Maximum number from the Tuple program: This can also be done using 2 methods

1. Using inbuilt function called max
2. Using loops

You’ll notice lists and tuple are almost same.

Using inbuilt function

tup=(10,8,99,22,11,5) #initializing tuple

maximum=max(tup) #it will return maximum number from the tuple

print("Maximum number from the tuple is",maximum)

Using loops:

tup=(10,22,1,98,2,43,100)

maximum=tup #putting the first value of tuple into variable maximum

for i in range(0, len(tup)): #iterating through the tuple from 0 to total length of the tuple

if tup[i]>maximum: #checking if next number is greater than the number saved

maximum=tup[i] #if yes then put that value into maximum

print ("Largest number from the tuple is ",maximum) #print the value

Minimum number from the tuple:

Using inbuilt function:

tup=[10,8,99,22,11,5] #initializing tup
minimum=min(tup) #it will return minimum number from the tuple
print("minimum number from the tuple is",minimum)

Using loop:

tup=(10,22,1,98,2,43,100)

minimum=tup #putting the first value of tuple into variable minimum

for i in range(0, len(tup)): #iterating through the tuple from 0 to total length of the tuple

if tup[i]<minimum: #checking if next number is smaller than the number saved

minimum=tup[i] #if yes then put that value into minimum

print ("Smallest number from the tuple is ",minimum) #print the value

Mean of numbers program:

tup=(2,44,12,53,22)

sum=0

for i in range(0,len(tup)):

sum=sum+tup[i] #it will add all the items from the tup

mean=sum/len(tup) #to find the mean sum of items is divided by total number of items

print("Mean of numbers is ", mean)

Linear search:

tup=(11,22,3,112,98,45,1)

print("Enter number you want to search")
num=eval(input()) #user enters the number he wants to search
flag=False
for i in range(0,len(tup)): #iterates through the tuple
if tup[i]==num: #checks every element with the number user entered if its equal it will print the message
print("Number found")

flag=True #flag will set to true and will break the loop

break

if flag==False: #if flag is still false means number is not found

Dictionary: Dictionary is a comma separated pair of key and value enclosed in curly braces. Each key is separated from its value by a colon [:]. Empty dictionary without any item is written with just two curly braces. Keys are unique in dictionary while values may not be. The values of a dictionary can be of any type. Key must be of immutable data type such as string, numbers or tuples. Let’s see an example of dictionary

dict= {‘Name’ : ’Mehak’, ‘Age’ : 15 ‘class’ : ‘10th’ }
print ("dict['Name']: ", dict['Name'])

print ("dict['Age']: ", dict['Age'])

Result of above example will be:

dict[‘Name’]: Mehak

dict[‘Age’]: 15

Basically these age name and class are keys and we can access the value associated with it using these keys.

Counting the frequency of elements in a list using a dictionary:

#initializing list
names = ['Physics', 'Chemistry', 'Physics', 'Biology', 'Math', 'Biology', 'Biology', 'Math', 'Chemistry']
d = {} #creating empty dictionary

for key in range(0,len(names)): #this loop will iterate through the list

count=0 #count will count the number of appearance of words

flag=False #flag will check if that word has already been counted or not

name = names[key]

for i in range(key, len(names)): #this loop will help us to compare the word with rest of the words in the list

if name not in d: #if name doesn't exist in the dictionary

d[name] = [] #it will add name to the dictionary

flag=True #this flag will indicate it is the first time that word has appeared

if name == names[i] and flag==True: #in this we'll check if name appears again in the list and is it for the ist time we are checking it

count+=1 #if it appears again count will increase

d[name]=count #and it will add count to that name

print(d) #displaying dictionary