Dictionary — Creating, Accessing, Adding, Modifying, Deleting

A dictionary stores data as key-value pairs, enclosed in curly braces {}. Keys must be unique and immutable (str, int, tuple); values can be any type.

Creating a Dictionary

empty = {}
student = {"name": "Riya", "age": 21, "course": "BCA"}
from_pairs = dict([("a", 1), ("b", 2)])
using_kwargs = dict(name="Amit", age=22)

Accessing Values

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

print(student["name"])         # 'Riya'
# print(student["marks"])      # KeyError: 'marks'

print(student.get("marks"))          # None (safe -- no error)
print(student.get("marks", "N/A"))    # 'N/A' (custom default)

Adding and Modifying Items

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

student["course"] = "BCA"       # adds a new key
print(student)                   # {'name': 'Riya', 'age': 21, 'course': 'BCA'}

student["age"] = 22               # modifies an existing key
print(student)                     # {'name': 'Riya', 'age': 22, 'course': 'BCA'}

Deleting Items

student = {"name": "Riya", "age": 21, "course": "BCA"}

del student["age"]            # removes key "age"
print(student)                 # {'name': 'Riya', 'course': 'BCA'}

removed = student.pop("course")   # removes & returns the value
print(removed, student)            # 'BCA' {'name': 'Riya'}

student.clear()                    # empties the dictionary
print(student)                      # {}

Iterating a Dictionary

student = {"name": "Riya", "age": 21, "course": "BCA"}

for key in student:                     # keys only
    print(key)

for key, value in student.items():       # keys and values
    print(key, ":", value)

for value in student.values():            # values only
    print(value)

Checking key existence

print("name" in student)       # True
print("marks" in student)      # False

Nested Dictionary

students = {
    "s1": {"name": "Riya", "marks": 92},
    "s2": {"name": "Amit", "marks": 78}
}
print(students["s1"]["name"])   # 'Riya'