This document outlines the characteristics and functionalities of dictionaries in Python, highlighting their use of key-value pairs and advantages like efficient lookups and dynamic sizing. It includes practical examples of creating, modifying, and deleting entries, as well as the usage of methods such as pop(). Additionally, it discusses the limitations on key types and introduces dictionary comprehensions for concise creation.

1. Dictionary in python

2. • 1. Dictionaries are built in data types in python
• 2. dictionaries are used to store the data in key : value pairs
• 3. Unlike other sequential data types which are indexed by a range of
numbers, dictionaries are indexed by keys.
• 4. keys in a dictionary can be any immutable type; like strings and
numbers.
• 5. Tuples can be used as keys if they contain only strings, numbers or
tuples .
• 6. If a tuple contains any mutable object either directly or indirectly it
cannot be used as a key.

3. • 7. you can not use lists as keys, since lists can be modified in place
using index assignments, slice assignments or methods like append()
and extend().
• 8. Mutable : We can add, remove, and change items after the
dictionary has been created.
• 9. Dynamic Size : Dictionaries can grow and shrink as needed, as we
can add or remove key value pair.
• 10. Efficient lookups : Dictionaries are implemented using hash tables,
providing average O(1) time Complexity For lookups, insertion, and
deletions.

4. • 11. Flexible Value Types: Values in a Dictionary can be of any
datatype, including other dictionaries, lists, sets, or even custom
objects.
• 12. Comprehensions: Python Supports dictionary comprehensions,
which allow you to create dictionaries in a concise and readable
manner.
13. Methods : Dictionaries come with a variety of buit-in methods for
operations like retrieving keys keys(), values(), item(),pop(). And more.

5. • # Creating a Dictionary
• My_dict = {'name' : “Ram", "age" : 30, "City" : "new York"}
• print(My_dict) #{'name': ‘Ram', 'age': 30, 'City': 'new York'}
• #adding a key – value pair
• My_dict[“job”] = “Engineer”
• print(My_dict) # {'name': ‘Ram', 'age': 30, 'City': 'new York', 'job': 'Engineer’}
#Modifying a value
• My_dict[“age”] = 31
• print(My_dict) # {'name': ‘Ram', 'age': 31, 'City': 'new York', 'job': 'Engineer’}
• #Removing a key value pair
• del My_dict[‘city’] # {'name': ‘Ram', 'age': 31, 'job': 'Engineer'}
• #checking if a key exists
• print(“name” in My-dict) #True

6. • #Iterating over keys and values
For key, value in My_dict.items():
print(f”{key} : {value}”)
# using a dictionary comprehension
Squares = {x: x*x for x in range(5)}
print(Squares)

7. Iterating over keys and values
for key, value in My_dict.items():
print(f"{key} : {value}")

8. Using a dictionary comprehension
• quares = {x: x*x for x in range(5)}
• print(squares)
• Output:
• {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

9. Pop() function
• In Python, the pop() method in dictionaries is used to remove a
specified key and return its corresponding value. If the specified key is
not found, the method can return a default value if provided, or raise
a KeyError if no default value is specified.
• dict.pop(key[, default])
• key: The key to be removed from the dictionary.
• default (optional): The value to return if the key is not found. If not
provided and the key is not found, a KeyError is raised.

10. Example
• # Define a dictionary
• my_dict = {'a': 1, 'b': 2, 'c': 3}
• # Remove and return the value for the key 'b'
• value = my_dict.pop('b')
• print(value) # Output: 2
• # Print the updated dictionary
• print(my_dict) # Output: {'a': 1, 'c': 3}

11. • # Define a dictionary
• my_dict = {'a': 1, 'b': 2, 'c': 3}
• # Attempt to remove and return the value for a non-existing key 'd' with a
default value
• value = my_dict.pop('d', 'Key not found')
• print(value) # Output: Key not found
• # Print the updated dictionary
• print(my_dict) # Output: {'a': 1, 'b': 2, 'c': 3}

12. • # Define a dictionary
• my_dict = {'a': 1, 'b': 2, 'c': 3}
• # Attempt to remove and return the value for a non-existing key 'd' with a default value
• value = my_dict.pop('d')
• print(value) # Output: Key not found
• # Print the updated dictionary
• print(my_dict) # Output: {'a': 1, 'b': 2, 'c': 3}
• Output: KeyError: ‘d’
• throw an exception and stop the execution .

13. Summary
• The pop() method removes the specified key from the dictionary and
returns its value.If the key is not found, it can return a default value if
provided; otherwise, it raises a KeyError.This method is useful for
safely removing and retrieving values from a dictionary.