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
delstatement or thepop()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: ADictionary 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/APython 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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