Explain the Python Dictionaries

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ICSM · Answer

1. What is a Dictionary in Python?
A dictionary is a built-in data type in Python that stores data in
key-value pairs.
Keys → must be unique and immutable (like strings, numbers, tuples).Values → can be of any data type (string, int, list, another dictionary, etc.).Dictionaries are unordered (before Python 3.7) but maintain 
insertion order from Python 3.7+.
2. Creating a Dictionary
# Empty dictionary
my_dict = {}
# Dictionary with key-value pairs
person = {
    "name": "Alice",
    "age": 25,
    "is_student": True
}
print(person)
# Output: {'name': 'Alice', 'age': 25, 'is_student': True}
3. Accessing Values
You get values by using the key:
print(person["name"])      # Alice
print(person["age"])       # 25
# Using get() avoids KeyError if key doesn't exist
print(person.get("grade")) # None
4. Adding / Updating Values
person["age"] = 26         # Update value
person["city"] = "London"  # Add new key-value pair
print(person)
# {'name': 'Alice', 'age': 26, 'is_student': True, 'city': 'London'}
5. Removing Items
person.pop("is_student")   # Removes a specific key
print(person)
del person["city"]         # Another way to delete
print(person)
person.clear()             # Removes all items
print(person)              # {}
6. Dictionary Methods
Some useful built-in methods:
person = {"name": "Alice", "age": 25, "city": "London"}
print(person.keys())    # dict_keys(['name', 'age', 'city'])
print(person.values())  # dict_values(['Alice', 25, 'London'])
print(person.items())   # dict_items([('name', 'Alice'), ('age', 25), ('city', 'London')])
# Looping
for key, value in person.items():
    print(key, ":", value)
7. Nesting Dictionaries
Dictionaries can hold other dictionaries:
students = {
    "s1": {"name": "Alice", "age": 20},
    "s2": {"name": "Bob", "age": 22}
}
print(students["s1"]["name"])  # Alice
8. Dictionary Comprehensions
Quickly build dictionaries:
squares = {x: x*x for x in range(1, 6)}
print(squares)  
# {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
Summary:
Dictionary = {key: value} pairs.Keys must be unique and immutable.Values can be anything.Supports adding, updating, deleting, nesting, and iteration.

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Explain the Python Dictionaries

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1 Answers

1. What is a Dictionary in Python?

2. Creating a Dictionary

3. Accessing Values

4. Adding / Updating Values

5. Removing Items

6. Dictionary Methods

7. Nesting Dictionaries

8. Dictionary Comprehensions

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