What is a Python Dictionary?

A dictionary is a collection which is unordered, changeable (mutable), and does not allow duplicates.

A dictionary in Python is a collection of key-value pairs. It is:

• Unordered (Python 3.6+ keeps insertion order)
• Changeable (Mutable)
• Indexed by keys
• No duplicate keys

Dictionaries are written with curly brackets, and they have keys and values:

my_dict = {
   "brand": "Ford",
   "model": "Mustang",
   "year": 1964
}
print(my_dict)

Output:

{'brand': 'Ford', 'model': 'Mustang', 'year': 1964}

Accessing Items

Access dictionary items by referring to their key:

my_dict = {
   "brand": "Ford",
   "model": "Mustang",
   "year": 1964
}
print(my_dict["model"])

Use .get() method for safe access:

my_dict = {
   "brand": "Ford",
   "model": "Mustang",
   "year": 1964
}
print(my_dict.get("year"))

Dictionary Keys

You can return the list of all keys using .keys():

To check if a key exists:

my_dict = {
   "brand": "Ford",
   "model": "Mustang",
   "year": 1964
}
if "model" in my_dict:
   print("Model key is present.")

Dictionary Values

Get all values in the dictionary:

my_dict = {
   "brand": "Ford",
   "model": "Mustang",
   "year": 1964
}
print(my_dict.values())

Output

dict_values(['Ford', 'Mustang', 1964])

Dictionary Items

Get all key-value pairs as tuples:

my_dict = {
   "brand": "Ford",
   "model": "Mustang",
   "year": 1964
}
print(my_dict.items())

Output

dict_items([('brand', 'Ford'), ('model', 'Mustang'), ('year', 1964)])

Add Dictionary Items

Add a new key-value pair:

my_dict = {
   "brand": "Ford",
   "model": "Mustang",
   "year": 1964
}
my_dict["color"] = "red"
print(my_dict)

Output

{'brand': 'Ford', 'model': 'Mustang', 'year': 1964, 'color': 'red'}

Change Dictionary Items

Update an existing item:

my_dict["year"] = 2024

Or use .update() method:

my_dict.update({"year": 2025})

Remove Dictionary Items

Remove by key:

my_dict.pop("model")

Remove last inserted item:

my_dict.popitem()

Remove a key using del:

del my_dict["brand"]

Clear all items:

my_dict.clear()

Loop Through Dictionaries

Loop through keys:

my_dict = {
   "brand": "Ford",
   "model": "Mustang",
   "year": 1964
}
for key in my_dict:
    print(key)

Output

brand
model
year

Loop through values:

my_dict = {
   "brand": "Ford",
   "model": "Mustang",
   "year": 1964
}
for value in my_dict.values():
    print(value)

Output

Ford
Mustang
1964

Loop through key-value pairs:

my_dict = {
   "brand": "Ford",
   "model": "Mustang",
   "year": 1964
}
for key, value in my_dict.items():
    print(key, "=", value)

Output

brand = Ford
model = Mustang
year = 1964

Copy a Dictionary

Use copy() or dict():

my_dict = {
   "brand": "Ford",
   "model": "Mustang",
   "year": 1964
}
x = my_dict.copy()
y = dict(my_dict)

Nested Dictionaries

A dictionary can contain other dictionaries:

my_family = {
 "child1": {"name": "Alice", "age": 10},
 "child2": {"name": "Bob", "age": 12}
}
print(my_family["child1"]["name"])

Output

Alice

Dictionary Constructor

You can also create dictionaries using the dict() constructor:

car = dict(brand="Ford", model="Mustang", year=1964)
print(car)

Output

{'brand': 'Ford', 'model': 'Mustang', 'year': 1964}

Python Dictionary Methods

Example 1: Creating a Dictionary

car = {
 "brand": "Ford",
 "model": "Mustang",
 "year": 1964
}
print(car)

Output:

{'brand': 'Ford', 'model': 'Mustang', 'year': 1964}

Explanation: We created a dictionary with 3 key-value pairs. Each key (like "brand") is associated with a value (like "Ford").

Example 2: Accessing Items

car = {
 "brand": "Ford",
 "model": "Mustang",
 "year": 1964
}
print(car["model"])         # Using key directly
print(car.get("year"))      # Using get() method

Output:

Mustang
1964

Explanation: The car["model"] fetches the value for the key "model", and get("year") does the same with safer handling if the key doesn't exist.

Example 3: Change Values

car = {
 "brand": "Ford",
 "model": "Mustang",
 "year": 1964
}
car["year"] = 2024
print(car)

Output

{'brand': 'Ford', 'model': 'Mustang', 'year': 2024}

Explanation: The value for the key "year" is updated from 1964 to 2024.

Example 4: Adding Items

car = {
 "brand": "Ford",
 "model": "Mustang",
 "year": 1964
}
car["color"] = "red"
print(car)

Output:

{'brand': 'Ford', 'model': 'Mustang', 'year': 2024, 'color': 'red'}

Explanation: A new key "color" is added to the dictionary with the value "red".

 Example 5: Loop Through Dictionary

car = {
 "brand": "Ford",
 "model": "Mustang",
 "year": 1964
}
for key, value in car.items():
   print(key, ":", value)

Output:

brand : Ford
model : Mustang
year : 2024
color : red

Explanation: .items() returns both key and value so we can print them in a loop.

Example 6: Check if Key Exists

car = {
 "brand": "Ford",
 "model": "Mustang",
 "year": 1964
}
if "model" in car:
   print("Yes, 'model' is a key.")

Output:

Yes, 'model' is a key.

Explanation: Checks for the presence of a specific key in the dictionary.

Example 7: Remove Items

car = {
 "brand": "Ford",
 "model": "Mustang",
 "year": 1964
}
car.pop("color")
print(car)

Output:

{'brand': 'Ford', 'model': 'Mustang', 'year': 2024}

Explanation: .pop() removes a key and its value.

Example 8: Dictionary Length

car = {
 "brand": "Ford",
 "model": "Mustang",
 "year": 1964
}
print(len(car))

Output:

3

Explanation: len() returns the number of key-value pairs in the dictionary.

Example 9: Copy a Dictionary

car = {
 "brand": "Ford",
 "model": "Mustang",
 "year": 1964
}
car_copy = car.copy()
print(car_copy)

Output:

{'brand': 'Ford', 'model': 'Mustang', 'year': 2024}

 Explanation: .copy() creates a shallow copy of the dictionary.

Example 10: Nested Dictionaries

family = {
 "child1": {"name": "Alice", "age": 10},
 "child2": {"name": "Bob", "age": 12}
}
print(family["child1"]["name"])

Output:

Alice

Explanation: This is a dictionary within a dictionary. Access nested data using multiple keys.

Example 11: Dictionary Comprehension

squares = {x: x*x for x in range(1, 6)}
print(squares)

Output:

{1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

Explanation: This is a compact way to create a dictionary using a loop.

Example 12: Dictionary Methods Summary

d = {"a": 1, "b": 2}
print(d.keys())         # dict_keys(['a', 'b'])
print(d.values())       # dict_values([1, 2])
print(d.items())        # dict_items([('a', 1), ('b', 2)])
print(d.get("a"))       # 1
d.update({"c": 3})
print(d)                # {'a': 1, 'b': 2, 'c': 3}

Conclusion

Dictionaries are one of Python’s most useful and flexible data structures. They’re perfect for representing real-world structured data like user profiles, configurations, JSON-like objects, and more.