Python Dictionaries

Python dictionaries are data structures that store key-value pairs. They are also known as associative arrays or hash maps in other programming languages. Dictionaries are unordered, mutable, and iterable objects in Python.

Here’s an example of a dictionary in Python:

python

student = {
    "name": "John Smith",
    "age": 20,
    "university": "ABC University",
    "major": "Computer Science"
}

In this example, "name", "age", "university", and "major" are keys, and "John Smith", 20, "ABC University", and "Computer Science" are their corresponding values.

You can access the values in a dictionary by using the keys:

python

print(student["name"])  # Output: John Smith
print(student["age"])   # Output: 20

You can also modify the values or add new key-value pairs to a dictionary:

python

student["age"] = 21  # Modifying the value
student["email"] = "[email protected]"  # Adding a new key-value pair

print(student["age"])    # Output: 21
print(student["email"])  # Output: [email protected]

To check if a key exists in a dictionary, you can use the in operator:

python

if "major" in student:
    print("Major:", student["major"])
else:
    print("Major not found")

You can iterate over the keys, values, or items (both keys and values) of a dictionary using loops:

python

# Iterating over keys
for key in student:
    print(key)

# Iterating over values
for value in student.values():
    print(value)

# Iterating over items
for key, value in student.items():
    print(key, ":", value)

Dictionaries are commonly used when you want to store and retrieve data using a meaningful key instead of numeric indices. They provide a flexible and efficient way to organize and access data.