Python Basics — Day 10 Dictionaries in Python

01. What is a Dictionary?

• A dictionary is a data structure that stores data as Key:Value pairs.

• Defined using curly braces {}.

student = {
    "name": "Sabin",
    "age": 35,
    "major": "Computer Science"
}

👉 Key Points:

• Keys must be immutable (e.g., strings, numbers, tuples).

• Values can be of any data type.

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02. Accessing Values

print(student["name"])   # Sabin
print(student["age"])    # 35

# Using .get() (returns None instead of error if key doesn’t exist)
print(student.get("major"))         # Computer Science
print(student.get("grade"))         # None
print(student.get("grade", "N/A"))  # Default value if key is missing

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03. Modifying & Adding Values

student["age"] = 31       # Modify existing value
student["grade"] = "A"    # Add new key
print(student)

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04. Deleting Values

del student["major"]      # Delete specific key
print(student)

grade = student.pop("grade", "N/A")   # Remove and return value
print("Removed value:", grade)

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05. Dictionary Methods

person = {"name": "Anna", "age": 22}

print(person.keys())    # dict_keys(['name', 'age'])
print(person.values())  # dict_values(['Anna', 22])
print(person.items())   # dict_items([('name', 'Anna'), ('age', 22)])

# Loop through dictionary
for k, v in person.items():
    print(k, ":", v)

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06. Nested Dictionaries

Dictionaries can contain other dictionaries.

students = {
    "s1": {"name": "Tom", "age": 20},
    "s2": {"name": "Anna", "age": 22}
}

print(students["s1"]["name"])   # Tom

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07. Practice Examples

Example 1: Print Student Info

student = {"name": "Sabin", "age": 35, "major": "CS"}

for k, v in student.items():
    print(f"{k}: {v}")

Example 2: Manage Scores

scores = {"German": 90, "English": 85, "Math": 80}
print("Total:", sum(scores.values()))
print("Average:", sum(scores.values()) / len(scores))