Dictionary Datatype In Python

Learn everything about Python dictionaries in this comprehensive guide. From key-value pairs to dictionary comprehension, master this essential Python data type today!

Key Characteristics of a Python Dictionary

1. Key-Value Pairs:

• A dictionary stores data as key-value pairs. The keys must be unique and immutable (like strings, numbers, or tuples), while the values can be of any data type and can repeat.

2. Mutable:

• You can change or update the values associated with a key, add new key-value pairs, or remove existing ones.

3. Efficient Lookups:

• Accessing a value via a key is a constant time operation (O(1)), making dictionaries very efficient for lookups.

Python Dictionary Creation

Dictionaries are created by using the curly braces {} or the dict() function.

Syntax: d = {key_01:value_01, key_02:value_02, …., key_N: value_N}

Empty python dictionary

d = {}
print(d)
print(type(d))

Output:

{}
<class ‘dict’>

Python Dictionary with key, value pairs

d = {1:"Ramesh", 2:"Arjun", 3:"Karthik"}
print(d) 

Output:

{1:"Ramesh", 2:"Arjun", 3:"Karthik"}

How to Add Items to a Dictionary

Syntax: d[key] = value

# Creating an empty dictionary
d = {}

# Adding entries to the dictionary
d[100] = "karthik"
d[200] = "ravi"
d[300] = "shiva"

print(d)

Output:

{100: 'karthik', 200: 'ravi', 300: 'shiva'}

Accessing Values in a Dictionary

• Keys are used to access values in a dictionary.
• The key acts as the identifier for the associated value.

# Dictionary with key-value pairs
student = {
    "name": "John",
    "age": 21,
    "course": "Computer Science"
}

# Accessing values using keys
print(student["name"])
print(student["age"])
print(student["course"])

Output:

John
21
Computer Science

If you try to access any key that doesn’t exist, Python raises a KeyError.

Common Dictionary Operations

Note: The reversed() function does not apply to dictionaries because they are unordered collections.

Examples Using All Functions Together

# Creating a dictionary
my_dict = {'name': 'Alice', 'age': 25, 'city': 'New York'}

# len() - Get the number of key-value pairs in the dictionary
print(f"Length of the dictionary: {len(my_dict)}")

# min() - Get the smallest key in the dictionary
print(f"Smallest key: {min(my_dict)}")

# max() - Get the largest key in the dictionary
print(f"Largest key: {max(my_dict)}")

# sorted() - Sort the keys and return a list
print(f"Sorted keys: {sorted(my_dict)}")

# reversed() - Not applicable, would raise an error if tried.

Output:

Length of the dictionary: 3
Smallest key: age
Largest key: name
Sorted keys: ['age', 'city', 'name']

Removing or Deleting Elements from a Dictionary

1. Using the del Keyword: remove specific keys from a dictionary using the del statement.
2. Using the clear() Method: remove all items from the dictionary, effectively clearing it.

# Creating a dictionary
d = {100: 'karthik', 200: 'ravi', 300: 'shiva'}

# Displaying the original dictionary
print("Original Dictionary:", d)

# Removing a specific key-value pair using del
del d[200]
print("After deleting key 200:", d)

# Clearing all items from the dictionary
d.clear()
print("After clearing the dictionary:", d)

Output:

Original Dictionary: {100: 'karthik', 200: 'ravi', 300: 'shiva'}
After deleting key 200: {100: 'karthik', 300: 'shiva'}
After clearing the dictionary: {}

Dictionary Methods

# Creating a dictionary
student = {
    'name': 'Alice',
    'age': 24,
    'major': 'Physics'
}

# Accessing a value
print(student['name'])

# Adding a new key-value pair
student['graduation_year'] = 2024
print(student)

# Updating a value
student['age'] = 25
print(student)

# Removing a key-value pair
student.pop('major')
print(student)

# Checking if a key exists
print('age' in student)

# Getting all keys, values, and key-value pairs
print(student.keys())
print(student.values())
print(student.items())

Output:

Alice
{'name': 'Alice', 'age': 24, 'major': 'Physics', 'graduation_year': 2024}
{'name': 'Alice', 'age': 25, 'major': 'Physics', 'graduation_year': 2024}
{'name': 'Alice', 'age': 25, 'graduation_year': 2024}
True
dict_keys(['name', 'age', 'graduation_year'])
dict_values(['Alice', 25, 2024])
dict_items([('name', 'Alice'), ('age', 25), ('graduation_year', 2024)])

Dictionary Comprehension

Dictionary comprehensions offer an best way to construct dictionaries in Python. Comprehensions consist of an expression, followed by a for clause, and can include optional conditionals.

Syntax: d = {key_expression: value_expression for item in iterable if cond}

Example:

# Creating a dictionary of squares
squares_dictionary = {x: x**2 for x in range(5)}
print(squares_dictionary )

# Creating a dictionary of squares for even numbers only
even_squares_dict = {x: x**2 for x in range(10) if x % 2 == 0}
print(even_squares_dict)

Output:

{0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
{0: 0, 2: 4, 4: 16, 6: 36, 8: 64}

Conclusion

Dictionaries are one of Python’s powerful and flexible data structures. They provide efficient access to data through key-value pairs and support a wide range of operations. Their ability to store heterogeneous data and handle dynamic data sizes makes them indispensable for many programming scenarios.

Knowledge Check

Related Article No.4

Check out our Trending Courses Demo Playlist

Kick Start Your Career With Our Data Job

Social Media channels

► KSR Datavizon Website :- https://www.datavizon.com
► KSR Datavizon LinkedIn :- https://www.linkedin.com/company/datavizon/
► KSR Datavizon You tube :- https://www.youtube.com/c/KSRDatavizon
► KSR Datavizon Twitter :- https://twitter.com/ksrdatavizon
► KSR Datavizon Instagram :- https://www.instagram.com/ksr_datavision
► KSR Datavizon Face book :- https://www.facebook.com/KSRConsultingServices
► KSR Datavizon Playstore :- https://play.google.com/store/apps/details?id=com.datavizon.courses&hl=en-IN
► KSR Datavizon Appstore :- https://apps.apple.com/in/app/ksr-datavizon/id1611034268