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🟢 Lesson 2 – Intermediate Level

🔹 Python Dictionaries: Storing and Accessing Key-Value Data

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🔰 What Is a Dictionary?

A dictionary in Python is a data structure that stores data in key-value pairs, like this:

pythonCopierModifierperson = {
    "name": "Ali",
    "age": 25,
    "city": "Rabat"
}

Each entry has:

• A key (like "name")
• A value (like "Ali")

📌 Dictionaries use curly braces {}, and keys must be unique.

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🧩 Why Use Dictionaries?

• 🔑 Easy to look up values using a key.
• ✅ Better for structured data (e.g. profiles, settings).
• ⚡ Faster than lists for some types of lookup operations.

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✅ Creating a Dictionary

pythonCopierModifierstudent = {
    "name": "Sara",
    "grade": "A",
    "age": 18
}

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🔍 Accessing Values

pythonCopierModifierprint(student["name"])     # Output: Sara
print(student["grade"])    # Output: A

🟥 ⚠️ If the key doesn’t exist, Python will raise a KeyError.

✅ Safer way using .get():

pythonCopierModifierprint(student.get("email", "Not provided"))

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🖊️ Adding or Updating Entries

pythonCopierModifierstudent["email"] = "sara@example.com"  # Add new key
student["grade"] = "A+"                # Update value

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❌ Removing Items

pythonCopierModifierstudent.pop("age")
print(student)

✅ Or delete by key:

pythonCopierModifierdel student["email"]

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🔁 Looping Through a Dictionary

📋 Loop through keys:

pythonCopierModifierfor key in student:
    print(key, "→", student[key])

📋 Loop through key-value pairs:

pythonCopierModifierfor key, value in student.items():
    print(f"{key}: {value}")

📋 Loop through just values:

pythonCopierModifierfor value in student.values():
    print(value)

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🧠 Dictionary Functions Summary:

Function	What It Does
dict.get(key, default)	Returns value or default if key missing
dict.items()	Returns key-value pairs
dict.keys()	Returns all keys
dict.values()	Returns all values
dict.pop(key)	Removes a key
key in dict	Checks if a key exists

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🧪 Exercise 1:

Write a program that:

• Creates a dictionary called contact.
• Asks the user to enter a name, phone, and email.
• Stores them as key-value pairs.
• Then prints the full contact information.

pythonCopierModifiercontact = {}

contact["name"] = input("Enter your name: ")
contact["phone"] = input("Enter your phone number: ")
contact["email"] = input("Enter your email address: ")

print("\n📇 Contact Information:")
for key, value in contact.items():
    print(f"{key.capitalize()}: {value}")

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🧪 Exercise 2 (Challenge):

Create a simple program to store multiple students and their grades.

pythonCopierModifierstudents = {}

for i in range(3):
    name = input(f"Enter student {i+1}'s name: ")
    grade = input(f"Enter {name}'s grade: ")
    students[name] = grade

print("\n🎓 Student Grades:")
for name, grade in students.items():
    print(f"{name}: {grade}")

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📝 Summary:

• Dictionaries store data in key-value pairs and are perfect for structured data.
• You can add, update, remove, and access values by their key.
• Looping over dictionaries is useful for displaying or processing structured data.

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