Introduction to Python Dictionaries

Dictionaries in Python are unordered, mutable, and indexed collections. They store data in key-value pairs and are highly efficient for lookup operations.
Syntax:

my_dict = {"key1": "value1", "key2": "value2"}

Key Features of Python Dictionaries

1. Keys: Must be unique and immutable (e.g., strings, numbers, tuples).
2. Values: Can be of any data type and duplicated.
3. Dynamic: Dictionaries grow or shrink as needed.
4. Fast Lookup: Keys are hashed, enabling rapid access.

Creating a Python Dictionary

You can create a dictionary using curly braces {} or the dict() constructor:

# Using curly braces
my_dict = {"name": "Alice", "age": 25}

# Using dict()
my_dict = dict(name="Alice", age=25)

Accessing Values

Access values using the key:

print(my_dict["name"])  # Output: Alice
print(my_dict.get("age"))  # Output: 25

Use .get() to avoid errors if the key doesn’t exist.

Modifying Dictionaries

• Add a key-value pair:

pythonCopyEditprint(my_dict["name"])  # Output: Alice
print(my_dict.get("age"))  # Output: 25

• Update a value:

my_dict["age"] = 26

Removing Items

• pop(key): Removes the specified key-value pair.
• popitem(): Removes the last inserted key-value pair.
• del: Deletes a key or the entire dictionary.

my_dict.pop("age")  
del my_dict["location"]

Dictionary Methods

Looping Through Dictionaries

Iterate over keys, values, or items:

# Loop through keys
for key in my_dict:
    print(key)

# Loop through values
for value in my_dict.values():
    print(value)

# Loop through items
for key, value in my_dict.items():
    print(key, value)

Nesting Dictionaries

Dictionaries can contain other dictionaries:

nested_dict = {
    "person1": {"name": "Alice", "age": 25},
    "person2": {"name": "Bob", "age": 30}
}nested_dict = {
    "person1": {"name": "Alice", "age": 25},
    "person2": {"name": "Bob", "age": 30}
}

Common Python Interview Questions (CIQ) on Dictionaries

How are dictionaries different from lists?

• Lists are ordered collections indexed by position, while dictionaries are unordered and indexed by keys

What happens if you use a mutable object as a dictionary key?

• Python raises a TypeError because dictionary keys must be immutable.

Explain the difference between pop() and popitem() methods in dictionaries.

• pop(key) removes the specified key-value pair, while popitem() removes the last inserted pair.

How can you merge two dictionaries in Python 3.9+?

• Use the | operator:pythonCopyEditmerged_dict = dict1 | dict2

Can a dictionary have duplicate keys?

• No, keys must be unique. If a key is duplicated, the last value assigned to it is retained.

Additional Resources

• Python Official Documentation on Dictionaries
• Python Dictionary Methods Guide
• Practice Problems on Dictionaries

Nested Dictionaries

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