Dictionaries in Python Class 11 Notes

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Teachers and Examiners (CBSESkillEduction) collaborated to create the Dictionaries in Python Class 11 Notes. All the important Information are taken from the NCERT Textbook Computer Science (083) class 11.

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Dictionaries in Python Class 11 Notes

Introduction to Dictionaries

A dictionary is a data structure that stores information in key-value pairs. In dictionary keys and values are separated by a colon (:) and different key-value pairs are separated by commas.

Creating a Dictionary

In Python, dictionaries are created using curly braces {}. Each item is a pair of key values that are separated by colons. Each key is linked to a value; keys and values are separated by a colon. Different key-value pairs are separated by commas.

Example –

dict3 = {'Mohan':95,'Ram':89,'Suhel':92,'Sangeeta':85}
print(dict3)

Output:
{'Mohan': 95, 'Ram': 89, 'Suhel': 92, 'Sangeeta': 85}
Accessing Items in a Dictionary

We have already seen how an approach known as indexing is used to retrieve the elements of a sequence (string, list, and tuple). The keys in a dictionary are used to access the objects rather than their indices or relative places. Each key corresponds to a value and acts as an index.

Example –

dict3 = {'Mohan':95,'Ram':89,'Suhel':92, 'Sangeeta':85}
print(dict3['Ram'])
print(dict3['Sangeeta'])

Output:
89
85
Dictionaries are Mutable

Dictionaries are mutable which implies that the contents of the dictionary can be changed after it has been created.

Adding a new item

We can add a new item to the dictionary as shown in the following example –

Example –

dict1 = {'Mohan':95,'Ram':89,'Suhel':92,'Sangeeta':85}
dict1['Meena'] = 78
print(dict1)

Output:
{'Mohan': 95, 'Ram': 89, 'Suhel': 92, 'Sangeeta': 85, 'Meena': 78}
Modifying an Existing Item

The existing dictionary can be modified by just overwriting the key-value pair. Example to modify a given item in the dictionary –

Example –

dict1 = {'Mohan':95,'Ram':89,'Suhel':92,'Sangeeta':85}
dict1['Suhel'] = 93.5
print(dict1)

Output:
{'Mohan': 95, 'Ram': 89, 'Suhel': 93.5, 'Sangeeta': 85}
Dictionary Operations
Membership

The membership operator in checks if the key is present in the dictionary and returns True, else it returns False.

Example –

dict1 = {'Mohan':95,'Ram':89,'Suhel':92,'Sangeeta':85}
print('Suhel' in dict1)

Output:
True

The not in operator returns True if the key is not present in the dictionary, else it returns False.

Example –

dict1 = {'Mohan':95,'Ram':89,'Suhel':92,'Sangeeta':85}
print('Suhel' not in dict1)

Output:
False
Traversing a Dictionary

We can access each item of the dictionary or traverse a dictionary using for loop.

Example –

dict1 ={'Mohan':95,'Ram':89,'Suhel':92,'Sangeeta':85}
for key in dict1:
    print(key,':',dict1[key])

Output:
Mohan : 95
Ram : 89
Suhel : 92
Sangeeta : 85

Dictionary methods and Built-in functions

Python provides many functions to work on dictionaries.

len()

Returns the length or number of key: value pairs of the dictionary passed as the argument.

Example –

dict1 = {'Mohan':95,'Ram':89,'Suhel':92, 'Sangeeta':85}
print(len(dict1))

Output:
4
dict()

Creates a dictionary from a sequence of key-value pairs.

Example –

pair1 = [('Mohan',95),('Ram',89),('Suhel',92),('Sangeeta',85)]
dict1 = dict(pair1)
print(dict1)

Output:
{'Mohan': 95, 'Ram': 89, 'Suhel': 92, 'Sangeeta': 85}
keys()

Returns a list of keys in the dictionary.

Example –

dict1 = {'Mohan':95, 'Ram':89,'Suhel':92, 'Sangeeta':85}
print(dict1.keys())

Output:
dict_keys(['Mohan', 'Ram', 'Suhel', 'Sangeeta'])
values()

Returns a list of values in the dictionary.

Example –

dict1 = {'Mohan':95, 'Ram':89,'Suhel':92, 'Sangeeta':85}
print(dict1.values())

Output:
dict_values([95, 89, 92, 85])
items()

Returns a list of tuples(key – value) pair

Example –

dict1 = {'Mohan':95, 'Ram':89,'Suhel':92, 'Sangeeta':85}
print(dict1.items())

Output:
dict_items([('Mohan', 95), ('Ram', 89), ('Suhel', 92), ('Sangeeta', 85)])
get()

Returns the value corresponding to the key passed as the argument.

Example –

dict1 = {'Mohan':95, 'Ram':89,'Suhel':92, 'Sangeeta':85}
print(dict1.get('Sangeeta'))

Output:
85
update()

appends the key-value pair of the dictionary passed as the argument to the key-value pair of the given dictionary.

Example –

dict1 = {'Mohan':95, 'Ram':89,'Suhel':92, 'Sangeeta':85}
dict2 = {'Sohan':79,'Geeta':89}
dict1.update(dict2)
print(dict1)
print(dict2)

Output:
{'Mohan': 95, 'Ram': 89, 'Suhel': 92, 'Sangeeta': 85, 'Sohan': 79, 'Geeta': 89}
{'Sohan': 79, 'Geeta': 89}
del()

Deletes the item with the given key To delete the dictionary from the memory we write: del Dict_name

Example –

dict1 = {'Mohan':95,'Ram':89,'Suhel':92, 'Sangeeta':85}
del dict1['Ram']
print(dict1)

Output:
{'Mohan': 95, 'Suhel': 92, 'Sangeeta': 85}
clear()

Deletes or clear all the items of the dictionary

Example –

dict1 = {'Mohan':95,'Ram':89,'Suhel':92, 'Sangeeta':85}
dict1.clear()
print(dict1)

Output:
{}
Computer Science Class 11 Notes
Computer Science Class 11 MCQ
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