Python Dictionaries

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Dictionaries are unordered collections of key-value pairs. They are useful for storing data that is associated with unique keys, allowing for fast and efficient lookups.


Creating Dictionaries

You can create a dictionary by placing key-value pairs inside curly braces {}, separated by commas. Each key is followed by a colon and its associated value.

Explanation of Code:

Dictionaries allow you to store and retrieve values using unique keys. Keys can be of immutable types such as strings and numbers, while values can be of any data type.

# Creating a dictionary
student = {
    "name": "Alice",
    "age": 21,
    "courses": ["Math", "Computer Science"]
}




Accessing Dictionary Items

You can access items in a dictionary by using their keys.

Explanation of Code:

Use the key inside square brackets to get the corresponding value from the dictionary.

# Accessing dictionary items
print(student["name"])  # Output: Alice
print(student["courses"])  # Output: ['Math', 'Computer Science']




Modifying Dictionary Items

Dictionaries are mutable, meaning you can change their items after creation.

Explanation of Code:

You can modify the value associated with a key by assigning a new value to that key.

# Modifying dictionary items
student["age"] = 22
student["courses"].append("Physics")
print(student)  # Output: {'name': 'Alice', 'age': 22, 'courses': ['Math', 'Computer Science', 'Physics']}




Adding and Removing Items

You can add new key-value pairs to a dictionary and remove existing ones.

  • To add a new item, assign a value to a new key.
  • To remove an item, use the del statement or the pop() method.
# Adding items to a dictionary
student["grade"] = "A"
print(student)  # Output: {'name': 'Alice', 'age': 22, 'courses': ['Math', 'Computer Science', 'Physics'], 'grade': 'A'}

# Removing items from a dictionary
del student["age"]
grade = student.pop("grade")
print(student)  # Output: {'name': 'Alice', 'courses': ['Math', 'Computer Science', 'Physics']}
print(grade)    # Output: A




Dictionary Methods

Python provides several built-in methods for dictionary manipulation.

  • keys(): Returns a list of keys in the dictionary.
  • values(): Returns a list of values in the dictionary.
  • items(): Returns a list of key-value pairs in the dictionary.
  • get(): Returns the value for a key, or a default value if the key is not found.
# Dictionary methods
keys = student.keys()
values = student.values()
items = student.items()
age = student.get("age", "N/A")

print("Keys:", keys)      # Output: Keys: dict_keys(['name', 'courses'])
print("Values:", values)  # Output: Values: dict_values(['Alice', ['Math', 'Computer Science', 'Physics']])
print("Items:", items)    # Output: Items: dict_items([('name', 'Alice'), ('courses', ['Math', 'Computer Science', 'Physics'])])
print("Age:", age)        # Output: Age: N/A




Python Dictionaries Example Code

Explanation of Code:

This program creates a dictionary of student information and demonstrates accessing, modifying, adding, removing items, and using dictionary methods.

# Creating a dictionary
student = {
    "name": "Alice",
    "age": 21,
    "courses": ["Math", "Computer Science"]
}

# Accessing dictionary items
print(student["name"])  # Output: Alice
print(student["courses"])  # Output: ['Math', 'Computer Science']

# Modifying dictionary items
student["age"] = 22
student["courses"].append("Physics")
print(student)  # Output: {'name': 'Alice', 'age': 22, 'courses': ['Math', 'Computer Science', 'Physics']}

# Adding items to a dictionary
student["grade"] = "A"
print(student)  # Output: {'name': 'Alice', 'age': 22, 'courses': ['Math', 'Computer Science', 'Physics'], 'grade': 'A'}

# Removing items from a dictionary
del student["age"]
grade = student.pop("grade")
print(student)  # Output: {'name': 'Alice', 'courses': ['Math', 'Computer Science', 'Physics']}
print(grade)    # Output: A

# Dictionary methods
keys = student.keys()
values = student.values()
items = student.items()
age = student.get("age", "N/A")

print("Keys:", keys)      # Output: Keys: dict_keys(['name', 'courses'])
print("Values:", values)  # Output: Values: dict_values(['Alice', ['Math', 'Computer Science', 'Physics']])
print("Items:", items)    # Output: Items: dict_items([('name', 'Alice'), ('courses', ['Math', 'Computer Science', 'Physics'])])
print("Age:", age)        # Output: Age: N/A




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