Basics of Using Python Dictionaries: Creating and Accessing Key-Value Pairs | Python tutorials on BeingSkilled

Dictionaries in Python are one of the most powerful and flexible data types. They are used to store data in the form of key-value pairs, allowing quick access to information based on a unique key.

This beginner-friendly guide will walk you through the basics of how to create dictionaries, how key-value pairs work, and how to access values using keys — all with simple and easy-to-follow examples.

1. What is a Dictionary?

A dictionary is a collection of unordered, mutable key-value pairs. Each key in the dictionary must be unique and immutable (like a string or a number), and it maps to a value that can be of any data type.

# Example 1: Creating a dictionary
person = {
    "name": "Rahul",
    "age": 28,
    "city": "Mumbai"
}
print(person)

2. Accessing Values with Keys

To retrieve a value from the dictionary, you use the key inside square brackets [] or the get() method.

# Example 2: Accessing values
print(person["name"])  # Rahul
print(person["age"])   # 28

# Example 3: Using get() method (safer)
print(person.get("city"))     # Mumbai
print(person.get("email"))    # None (instead of error)

3. Adding New Key-Value Pairs

You can add new pairs simply by assigning a value to a new key.

# Example 4: Adding a new key
person["email"] = "rahul@example.com"
print(person)

4. Updating Existing Values

To update a value, use the key and assign a new value to it.

# Example 5: Updating a value
person["city"] = "Delhi"
print(person)

5. Keys Must Be Unique

Keys in a dictionary must be unique. If you define the same key more than once, the last assignment will overwrite the previous one.

# Example 6: Duplicate keys
data = {
    "id": 101,
    "id": 102
}
print(data)  # {'id': 102}

6. Dictionary with Different Data Types

Values in a dictionary can be any data type — strings, numbers, lists, even other dictionaries.

# Example 7
info = {
    "name": "Anu",
    "scores": [85, 90, 88],
    "details": {
        "grade": "A",
        "active": True
    }
}
print(info["scores"])
print(info["details"]["grade"])

7. Empty Dictionary

You can create an empty dictionary and add values later.

# Example 8
user = {}
user["username"] = "user123"
user["status"] = "active"
print(user)

8. Dictionary Length

Use len() to get the number of key-value pairs in the dictionary.

# Example 9
print(len(person))  # Number of key-value pairs

Best Practices for Working with Dictionaries

Use descriptive keys that make your data readable.
Use get() when accessing values if you're unsure whether the key exists.
Use dictionaries when you need a logical association between a key and its value.

Common Use Cases

Storing user profiles or settings
Mapping names to scores or IDs
Representing structured data (e.g., from JSON)

Summary

Dictionaries store data using key-value pairs.
Keys must be unique and immutable, values can be of any type.
You can access, add, and update data using keys.
Dictionaries are ideal for quick lookups and storing structured information.

Final Thoughts

Once you're comfortable creating and accessing key-value pairs, you'll find dictionaries to be one of the most useful tools in your Python toolkit. They are efficient, flexible, and perfect for organizing data clearly and logically.

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