Creating Dictionaries

Dictionaries in Python are established using curly braces {}, containing key-value pairs that are separated by colons. For example, to create a dictionary named person:

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

In this instance, the dictionary person holds three key-value pairs: name is linked to Alice, age is linked to 30, and city is linked to New York.

Accessing Dictionary Values

To retrieve a value associated with a specific key in a dictionary, square bracket notation can be used:

print(person['name']) # Output: Alice

print(person['age']) # Output: 30

Attempting to access a nonexistent key will result in a KeyError. To avoid this, the get() method can be employed, which returns None (or a specified default value) if the key isn't found:

print(person.get('job', 'Unknown')) # Output: Unknown

Modifying Dictionaries

You can freely add, change, or eliminate key-value pairs in a dictionary:

To add a new entry:

person['job'] = 'Engineer'

print(person) # Output: {'name': 'Alice', 'age': 30, 'city': 'New York', 'job': 'Engineer'}

To alter an existing value:

person['age'] = 31

print(person) # Output: {'name': 'Alice', 'age': 31, 'city': 'New York', 'job': 'Engineer'}

To delete a key-value pair, use either the del keyword or the pop() method:

del person['city']

print(person) # Output: {'name': 'Alice', 'age': 31, 'job': 'Engineer'}

removed_value = person.pop('job')

print(person) # Output: {'name': 'Alice', 'age': 31}

print(removed_value) # Output: Engineer

Dictionary Methods

Python dictionaries come equipped with several built-in methods that simplify operations. Here are some frequently used methods:

• keys(): Provides a view of all keys in the dictionary.
• values(): Returns a view of all values in the dictionary.
• items(): Yields a view of key-value pairs in the dictionary as tuples.
• update(): Combines a dictionary with another dictionary or iterable of key-value pairs.
• clear(): Deletes all key-value pairs from the dictionary.

Here are a few examples:

print(person.keys()) # Output: dict_keys(['name', 'age'])

print(person.values()) # Output: dict_values(['Alice', 31])

print(person.items()) # Output: dict_items([('name', 'Alice'), ('age', 31)])

person.update({'city': 'San Francisco', 'job': 'Engineer'})

print(person) # Output: {'name': 'Alice', 'age': 31, 'city': 'San Francisco', 'job': 'Engineer'}

person.clear()

print(person) # Output: {}

Dictionaries are incredibly adaptable and serve a multitude of purposes, ranging from basic data storage to sophisticated structures like graphs and trees. Their straightforward syntax and powerful built-in methods make them invaluable for data management in Python, making them a must-have tool for any programmer.