Python Dictionaries

Creating a Dictionary

You create a dictionary with curly braces, writing each key and value separated by a colon. Keys must be unique and immutable, such as a string, number, or tuple.

student = {
    "name": "Aarav",
    "age": 21,
    "course": "B.Tech"
}
print(student)

Accessing Values

Access a value with square-bracket key lookup, or use get(), which returns None (or a default you supply) instead of raising an error when the key is missing.

student = {"name": "Aarav", "age": 21}

print(student["name"])          # Aarav
print(student.get("city"))      # None
print(student.get("city", "NA")) # NA

Adding, Updating and Deleting

Assign to a new key to add it, or to an existing key to update its value. del and pop() remove a key — pop() also returns the value that was removed, which is handy inside functions.

student = {"name": "Aarav", "age": 21}

student["age"] = 22          # update
student["city"] = "Delhi"    # add
del student["city"]          # delete
age = student.pop("age")     # remove and return
print(student, age)

Iterating Over a Dictionary

keys() returns all keys, values() returns all values, and items() returns key-value pairs — items() is the most common choice inside a for loop.

student = {"name": "Aarav", "age": 21, "course": "B.Tech"}

for key, value in student.items():
    print(key, "->", value)

Why Use a Dictionary?

• Fast lookup by a meaningful key instead of a numeric index.
• Modelling real-world records, like a JSON API response or a database row.
• Counting occurrences, grouping data, or building simple caches.