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4.2 Dictionaries – Understanding Dictionaries, Dictionary Operations

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Wellcome to this insightful lesson where we’ll explore the powerful world of dictionaries in Python. Dictionaries are versatile data structures that allow us to store and retrieve data using key-value pairs. In this lesson, we’ll dive into the fundamentals of dictionaries, understand their structure, and explore various operations that can be performed on dictionaries.

Understanding Dictionaries:

1. Definition:

  • A dictionary is a collection of unordered, mutable, and indexed elements.
  • Elements are stored as key-value pairs, where each key must be unique.
  • Syntax:
my_dict = {"key1": value1, "key2": value2, ...}

2. Accessing Values:

  • Values can be accessed using their respective keys.
  • Example:
my_dict = {"name": "Alice", "age": 25, "city": "Wonderland"}
print("Name:", my_dict["name"])

3. Modifying Values:

  • Values associated with a key can be modified.
  • Example:
my_dict = {"name": "Alice", "age": 25, "city": "Wonderland"}
my_dict["age"] = 26

Dictionary Operations:

4. Adding Key-Value Pairs:

  • New key-value pairs can be added to a dictionary.
  • Example:
my_dict = {"name": "Alice", "age": 25}
my_dict["city"] = "Wonderland"

5. Removing Key-Value Pairs:

  • Key-value pairs can be removed using the del keyword or the pop() method.
  • Example:
my_dict = {"name": "Alice", "age": 25, "city": "Wonderland"}
del my_dict["age"]

6. Dictionary Methods:

  • Dictionaries have various built-in methods, such as keys(), values(), and items().
  • Example:
my_dict = {"name": "Alice", "age": 25, "city": "Wonderland"}
keys_list = my_dict.keys()
values_list = my_dict.values()

7. Dictionary Iteration:

  • Iterating through keys, values, or key-value pairs.
  • Example:
my_dict = {"name": "Alice", "age": 25, "city": "Wonderland"}
for key in my_dict:
    print(f"Key: {key}, Value: {my_dict[key]}")

Example:

Let’s consider an example where we use a dictionary to store information about a person:

# Example Code
person_info = {"name": "Bob", "age": 30, "occupation": "Engineer"}

# Accessing values
print("Name:", person_info["name"])
print("Age:", person_info["age"])

# Modifying a value
person_info["age"] = 31

# Adding a new key-value pair
person_info["location"] = "Cityville"

# Removing a key-value pair
del person_info["occupation"]

# Iterating through keys and values
for key, value in person_info.items():
    print(f"{key}: {value}")

Practice Exercise:

Create a Python script that uses a dictionary to represent a product in an online store. Include keys such as “product_name,” “price,” and “quantity_available.” Perform operations like modifying the price, adding a discount, and updating the quantity available.

# Example Practice Exercise
product_info = {"product_name": "Laptop", "price": 1200, "quantity_available": 50}

# Modifying the price
product_info["price"] = 1100

# Adding a discount
discount = 100
product_info["price_with_discount"] = product_info["price"] - discount

# Updating the quantity available
new_quantity = 40
product_info["quantity_available"] = new_quantity

# Displaying the updated information
for key, value in product_info.items():
    print(f"{key}: {value}")

Summary:

In this lesson, we’ve explored the fundamentals of dictionaries in Python and learned how to perform various operations on them. Dictionaries provide a flexible and efficient way to manage data using key-value pairs. Practice using dictionaries to enhance your coding skills, and feel free to ask questions in the discussion forum. Let’s continue our Python journey with confidence in utilizing dictionaries!

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