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Introduction
A sample program
Tokens
Datatypes
variables
Inputs and Outputs
Expressions
Blocks
Handling decisions
Loops
Break and Continue
Strings
Lists
Tuples
Dictionaries
Functions

Dictionaries:

Dictionaries in Python

In Python, dictionaries are a built-in data type that allows you to store collections of key-value pairs. Dictionaries are mutable, meaning you can change their contents after they are created.

Creating Dictionaries

There are several ways to create dictionaries in Python:

Using curly braces `{}`

my_dict = {'key1': 'value1', 'key2': 'value2'}

Using the `dict()` constructor

my_dict = dict(key1='value1', key2='value2')

Using a list of tuples

my_dict = dict([('key1', 'value1'), ('key2', 'value2')])

Using a list of lists

my_dict = dict([['key1', 'value1'], ['key2', 'value2']])

Using the `zip()` function

keys = ['key1', 'key2'] values = ['value1', 'value2'] my_dict = dict(zip(keys, values))

Major Operations on Dictionaries

Accessing Values

value = my_dict['key1']

Adding or Updating Values

my_dict['key3'] = 'value3' my_dict['key1'] = 'new_value1'

Deleting Key-Value Pairs

del my_dict['key1']

Checking for Keys

if 'key1' in my_dict: print("Key exists")

Iterating Through Keys and Values

for key, value in my_dict.items(): print(key, value)

Getting Keys and Values Separately

keys = my_dict.keys() values = my_dict.values()

Copying a Dictionary

new_dict = my_dict.copy()

Merging Dictionaries

dict1 = {'a': 1, 'b': 2} dict2 = {'b': 3, 'c': 4} merged_dict = {**dict1, **dict2}

Using Default Values

value = my_dict.get('nonexistent_key', 'default_value')

Removing and Returning a Key-Value Pair

value = my_dict.pop('key1', 'default_value')

Clearing All Key-Value Pairs

my_dict.clear()

Example Usage

# Creating a dictionary person = { 'name': 'Alice', 'age': 30, 'city': 'New York' } # Accessing values print(person['name']) # Alice # Adding a new key-value pair person['email'] = 'alice@example.com' # Updating an existing value person['age'] = 31 # Deleting a key-value pair del person['city'] # Iterating through the dictionary for key, value in person.items(): print(f"{key}: {value}") # Checking for a key if 'name' in person: print("Name exists in the dictionary")