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🧾 Python Dictionaries – Access, Update, Loop & Nested Dictionary Examples

🧲 Introduction – Why Use Dictionaries in Python?

A dictionary in Python is an unordered collection of data stored in key-value pairs. Unlike lists that use numeric indexes, dictionaries use keys, which can be strings, numbers, or tuples. They’re ideal for representing structured data like JSON, configuration files, or database records.

🎯 In this guide, you’ll learn:

How to create and manage dictionaries
How to view, loop, and manipulate dictionary data
Common methods for working with dictionaries
Real-world usage through practice exercises

📌 Topics Covered

🧩 Topic	📘 Description
Dictionary: Access / Change / Add / Remove	Get, update, insert, or delete dictionary entries
Dictionary: View Objects	Explore `.keys()`, `.values()`, `.items()`
Loop Dictionaries	Iterate through keys, values, or both
Copy / Nested Dictionaries	Create copies and nested structures
Dictionary Methods	Built-in methods like `get()`, `pop()`, `update()`, `clear()`
Dictionary Exercises	Practice problems to reinforce learning

🔧 Python Dictionary: Access / Change / Add / Remove Items

🔹 Creating a Dictionary

person = {
  "name": "Alice",
  "age": 30,
  "city": "New York"
}

🔹 Accessing Items

print(person["name"])     # Alice
print(person.get("age"))  # 30

🔹 Changing Items

person["city"] = "Boston"

🔹 Adding Items

person["email"] = "alice@example.com"

🔹 Removing Items

person.pop("age")
del person["city"]

🔍 Python Dictionary: View Objects

Dictionaries allow access to three types of view objects:

print(person.keys())    # dict_keys(['name', 'email'])
print(person.values())  # dict_values(['Alice', 'alice@example.com'])
print(person.items())   # dict_items([('name', 'Alice'), ('email', 'alice@example.com')])

✅ These return dynamic views that update when the dictionary changes.

🔁 Python Dictionary: Loop Dictionaries

🔹 Loop through keys

for key in person:
    print(key)

🔹 Loop through values

for value in person.values():
    print(value)

🔹 Loop through key-value pairs

for key, value in person.items():
    print(f"{key} = {value}")

🧳 Python Copy / Nested Dictionaries

🔹 Copying a Dictionary

copy_person = person.copy()

🔹 Nested Dictionaries

family = {
  "child1": {"name": "Anna", "age": 5},
  "child2": {"name": "Tom", "age": 8}
}
print(family["child1"]["name"])  # Anna

🛠️ Python Dictionary Methods

Method	Description
`get()`	Safely get a value
`update()`	Merge another dict or key-value pairs
`pop()`	Remove a key and return its value
`popitem()`	Remove the last inserted item
`setdefault()`	Get value or set default
`clear()`	Remove all items
`copy()`	Return a shallow copy

🧪 Python Dictionary Exercises

✅ 1. Access and print value by key

student = {"name": "Bob", "grade": "A"}
print(student["grade"])  # A

✅ 2. Update and add new item

student["grade"] = "B"
student["passed"] = True
print(student)

✅ 3. Loop through dictionary

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

✅ 4. Create a nested dictionary

contacts = {
  "john": {"phone": "123", "email": "john@example.com"},
  "jane": {"phone": "456", "email": "jane@example.com"}
}
print(contacts["jane"]["email"])  # jane@example.com

📌 Summary – Recap & Next Steps

Python dictionaries provide a flexible and powerful way to work with structured data. With efficient access and built-in methods, dictionaries are widely used in everything from data processing to API responses.

🔍 Key Takeaways:

Dictionaries store data in key-value pairs.
Use .get(), .pop(), and .update() for safe data manipulation.
Nested dictionaries help structure complex information.
Loops help you efficiently traverse dictionary items.

⚙️ Real-World Relevance:
Used heavily in configuration files, databases, APIs (like JSON), and applications where data must be associated by name or ID.

❓ FAQ – Python Dictionaries

❓ What is a Python dictionary?
✅ A dictionary is a collection of key-value pairs. Keys must be unique and immutable (e.g., strings, numbers, tuples).

❓ Can you have duplicate keys in a dictionary?
✅ No. Later assignments overwrite earlier ones.

❓ How do you safely get a value without a KeyError?
✅ Use .get() instead of square brackets:

value = mydict.get("key", "default")

❓ Can you nest dictionaries inside each other?
✅ Yes. You can have dictionaries within dictionaries to model complex structures.

❓ What is the difference between .pop() and del?
✅ .pop() returns the value and is safer. del just removes the key.

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