Python - Dictionaries

Dictionaries in Python: Unraveling Key-Value Pairs

Dictionaries in Python are powerful data structures that store key-value pairs, allowing efficient retrieval and manipulation of data. Understanding dictionaries is crucial for tasks like representing real-world entities, configuration settings, and more. Let's delve into the characteristics and functionalities of dictionaries:

1. Dictionary Declaration :

   - Dictionaries are declared using curly braces {} and consist of key-value pairs separated by colons.

 
# Dictionary Declaration Example

person = {'name': 'Sakib', 'age': 32, 'city': 'Dhaka'}  # Dictionary with key-value pairs

# Output:
print(person)  # {'name': 'Sakib', 'age': 32, 'city': 'Dhaka'}

# Accessing values using keys
print(person['name'])  # Sakib
     

    

2. Key-Value Pairs :

   - Each element in a dictionary is a key-value pair, where keys are unique and used for indexing.

        
# Key-Value Pairs in a Dictionary Example

person = {'name': 'Rakib', 'age': 28, 'city': 'Rajshahi'}  # Dictionary with key-value pairs

# Output:

print(person)  # {'name': 'Rakib', 'age': 28, 'city': 'Rajshahi'}

# Accessing values using keys
print(person['name'])  # Rakib
print(person['age'])  # 28
      

    

3. Dictionary Methods :

   - Python provides a variety of built-in methods for dictionary manipulation, including adding items, removing keys, and updating values.

  
# Dictionary Methods Example

person = {'name': 'Sohel', 'age': 26, 'city': 'Rangpur'}  # Dictionary with key-value pairs

# Output:

print(person.keys())  # dict_keys(['name', 'age', 'city'])

print(person.values())  # dict_values(['Sohel', 26, 'Rangpur'])

print(person.items())  # dict_items([('name', 'Sohel'), ('age', 26), ('city', 'Rangpur')])

# Adding a new key-value pair
person.update({'gender': 'Male'})

# Output:
print(person)  # {'name': 'Sohel', 'age': 26, 'city': 'Rangpur', 'gender': 'Male'}
      

    

4. Iterating Through Dictionaries :

   - You can iterate through keys, values, or both using methods like keys(), values(), and items().

# Iterating Through a Dictionary Example

person = {'name': 'Ratul', 'age': 26, 'city': 'Cumilla'}  # Dictionary with key-value pairs

# Output:

# Iterating through keys
for key in person:
    print(key, person[key])  # Outputs: name Ratul, age 26, city Cumilla

# Iterating through values
for value in person.values():
    print(value)  # Outputs: Ratul, 26, Cumilla

# Iterating through key-value pairs
for key, value in person.items():
    print(key, value)  # Outputs: name Ratul, age 26, city Cumilla
      

    

5. Nested Dictionaries :

   - Dictionaries can be nested, allowing the representation of complex data structures.

# Nested Dictionaries Example

people = {'person1' : {'name' : 'Fahim' , 'age' : 27, 'city' : 'Barishal'},
         'person2': {'name': 'Safin', 'age': 24, 'city': 'Bhola'}}

# Accessing nested values
print(people['person1']['name'])  # Output: Fahim

print(people['person2']['age'])  # Output: 24


# Modifying nested values
people['person1']['city'] = 'Pirojpur'

print(people['person1']['city'])  # Output: Pirojpur
      

 

6. Dictionary Comprehensions :

   - Similar to lists and sets, dictionary comprehensions provide a concise way to create dictionaries based on existing sequences.

# Dictionary Comprehensions Example

# Creating a dictionary of squares using dictionary comprehensions

squares = {x: x**2 for x in range(1, 7)}  # Output: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36}

# Filtering dictionary items using a condition

even_squares = {x: x**2 for x in range(1, 6) if x % 2 == 0}  # Output: {2: 4, 4: 16, 6: 36}
      

     
Understanding dictionaries enables you to efficiently manage data with key-value relationships, offering a flexible and dynamic approach to organizing and accessing information in your Python programs. Whether you're building a database, managing configurations, or representing entities, dictionaries provide a versatile solution.