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Home Interviews Explain the Python Dictionaries – MindStick
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1 Answers

ICSM Computer
ICSM Computer 22 Sep 2025
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1. What is a Dictionary in Python?

A dictionary is a built-in data type in Python that stores data in key-value pairs.

  • Keys → must be unique and immutable (like strings, numbers, tuples).
  • Values → can be of any data type (string, int, list, another dictionary, etc.).
  • Dictionaries are unordered (before Python 3.7) but maintain insertion order from Python 3.7+.

2. Creating a Dictionary

# Empty dictionary
my_dict = {}

# Dictionary with key-value pairs
person = {
    "name": "Alice",
    "age": 25,
    "is_student": True
}
print(person)
# Output: {'name': 'Alice', 'age': 25, 'is_student': True}

3. Accessing Values

You get values by using the key:

print(person["name"])      # Alice
print(person["age"])       # 25

# Using get() avoids KeyError if key doesn't exist
print(person.get("grade")) # None

4. Adding / Updating Values

person["age"] = 26         # Update value
person["city"] = "London"  # Add new key-value pair
print(person)
# {'name': 'Alice', 'age': 26, 'is_student': True, 'city': 'London'}

5. Removing Items

person.pop("is_student")   # Removes a specific key
print(person)

del person["city"]         # Another way to delete
print(person)

person.clear()             # Removes all items
print(person)              # {}

6. Dictionary Methods

Some useful built-in methods:

person = {"name": "Alice", "age": 25, "city": "London"}

print(person.keys())    # dict_keys(['name', 'age', 'city'])
print(person.values())  # dict_values(['Alice', 25, 'London'])
print(person.items())   # dict_items([('name', 'Alice'), ('age', 25), ('city', 'London')])

# Looping
for key, value in person.items():
    print(key, ":", value)

7. Nesting Dictionaries

Dictionaries can hold other dictionaries:

students = {
    "s1": {"name": "Alice", "age": 20},
    "s2": {"name": "Bob", "age": 22}
}
print(students["s1"]["name"])  # Alice

8. Dictionary Comprehensions

Quickly build dictionaries:

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

Summary:

  • Dictionary = {key: value} pairs.
  • Keys must be unique & immutable.
  • Values can be anything.
  • Supports adding, updating, deleting, nesting, and iteration.
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