Python Dictionaries

Python Dictionaries

Introduction

Dictionaries are one of Python’s most powerful and flexible built-in data types. Unlike lists or tuples, which store values based on index positions, dictionaries store data as key-value pairs.

In this tutorial, you’ll learn how to create, access, modify, and use dictionaries in Python with practical examples.

What Is a Dictionary in Python?

A dictionary is a collection of unordered, mutable, and indexed data in Python. It is written using curly braces {} and contains key-value pairs.

Syntax:

my_dict = {
    "name": "Alice",
    "age": 25,
    "city": "New York"
}

Dictionary Characteristics

• Unordered (Python < 3.7), but insertion-ordered in Python 3.7+
• Mutable: You can add, modify, or remove key-value pairs.
• Keys must be unique and immutable (strings, numbers, tuples).
• Values can be of any data type, and duplicates are allowed.

Creating a Dictionary

Example 1: Using curly braces

student = {
    "name": "John",
    "grade": "A",
    "passed": True
}

Example 2: Using the dict() constructor

employee = dict(name="Emma", position="Manager", salary=75000)

Accessing Dictionary Items

You can access values using their keys:

print(student["name"])        # Output: John
print(employee["position"])   # Output: Manager

To avoid errors when a key doesn’t exist, use the get() method:

print(student.get("age", "Not specified"))  # Output: Not specified

Adding or Modifying Items

Adding a new key-value pair:

student["age"] = 20

Modifying an existing value:

student["grade"] = "A+"

Removing Dictionary Items

Using pop():

student.pop("passed")  # Removes the key 'passed'

Using del:

del student["grade"]

Using clear():

student.clear()  # Empties the dictionary

Looping Through a Dictionary

Loop through keys:

for key in employee:
    print(key)

Loop through values:

for value in employee.values():
    print(value)

Loop through key-value pairs:

for key, value in employee.items():
    print(key, ":", value)

Dictionary Methods

Example:

person = {"name": "Lily", "age": 30}
person.update({"city": "Boston"})
print(person)

Nested Dictionaries

Dictionaries can contain other dictionaries.

students = {
    "101": {"name": "Alex", "grade": "B"},
    "102": {"name": "Maya", "grade": "A"}
}

print(students["101"]["name"])  # Output: Alex

Dictionary Comprehension

Python supports dictionary comprehension, a concise way to create dictionaries.

Example:

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

Use Cases of Dictionaries

• Storing user profiles (e.g., name, age, location)
• Counting elements (e.g., word frequency)
• Mapping keys to functions or operations
• Storing structured data

Conclusion

Python dictionaries are a flexible and efficient way to store and manage key-value pairs. They are extremely useful for organizing data, making lookups, and simplifying many coding tasks.

By mastering dictionaries, you unlock the full potential of Python’s data manipulation capabilities.

Frequently Asked Questions

Q1: Can dictionary keys be of any data type?
No. Keys must be immutable types like strings, numbers, or tuples.

Q2: Are dictionaries ordered?
Yes, as of Python 3.7+, dictionaries preserve insertion order.

Q3: Can a dictionary have duplicate keys?
No. Keys must be unique. If a duplicate key is added, the latest value will overwrite the previous one.

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#python #pythondictionaries #dictionarypython #keyvaluepairs #pythontutorial #pythonforbeginners #learnpython #dictionarystorage #pythondatatypes