Python dictionary

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• A dictionary is mutable and is another container
type that can store any number of Python objects
• Dictionaries consist of pairs (called items) of keys
and their corresponding values.
• Python dictionaries are also known as associative
arrays or hash tables.
• The general syntax of a dictionary is as follows:
Dog = {‘name': ‘Marley', ‘color': ‘Gold', ‘legs': ‘4'}
or
Dog=dict(name=“Marley", color=“Gold”,legs=4);
Python Dictionary:

Python Dictionary Features:
• Each key is separated from its value by a colon (:).
• The items are separated by commas, and the whole thing is enclosed
in curly braces.
• An empty dictionary without any items is written with just two curly
braces, like this: {}.
• Keys are unique within a dictionary while values may not be

Accessing in Dictionary:
• d.items()
• d.values()
• d.keys()

Accessing Values in Dictionary:
• To access dictionary elements, you can use the familiar square
brackets along with the key to obtain its value.
• For example:
student = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
print (“student['Name']: ", student['Name'])
● Output: student['Name']: Zara

Updating Dictionary:
• You can update a dictionary by adding a new entry or item (i.e., a key-value
pair)
• modifying an existing entry, or deleting an existing entry as shown below in
the simple example
• student = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
student['Age'] = 8; # update existing entry
student['School'] = "DPS School"; # Add new entry
print (“student['Age']: ", student['Age'])
print (“student['School']: ", student['School'])
• Output: student['Age']: 8 student['School']: DPS School

Delete Dictionary Elements:
• You can either remove individual dictionary elements or clear the entire
contents of a dictionary
• To explicitly remove an entire dictionary, just use the del statement. i.e:
student = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
• del student['Name']; # remove entry with key 'Name'
• student.clear(); # remove all entries in student del student ; # delete
entire dictionary
• print (“student['Age']: ", student['Age'])
• print (“student['School']: ", student['School'])

Properties of Dictionary Keys:
There are two important points to remember about dictionary keys:
(a) More than one entry per key not allowed. Which means no duplicate key is allowed.
When duplicate keys encountered during assignment, the last assignment wins.
• student= {'Name': 'Zara', 'Age': 7, 'Name': 'Manni'};
• print (“student['Name']: ", student['Name']) //Output: student['Name']: Manni
(b) Keys must be immutable. Which means you can use strings or numbers as
dictionary keys but something like ['key'] is not allowed. Following is a simple example:
• student = {['Name']: 'Zara', 'Age': 7};
• print (student['Name']: ", student['Name']) //TypeError

Let’s Practice .. !
Problem I
• Write a Python program to check if a given
key already exists in a dictionary.
Problem II
. Write a Python program to remove duplicates
from Dictionary

Python dictionary

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