Python Dictionary: A Comprehensive Knowledge Summary

Python dictionaries are one of the most versatile and frequently used data structures in Python programming. They provide a way to store and access data in key-value pairs, making them ideal for scenarios where data retrieval based on a unique key is necessary. In this article, we will summarize key knowledge points about Python dictionaries, covering their creation, manipulation, and useful methods.
‌Creation of Dictionaries‌

Dictionaries can be created using curly braces {} with each item being a key-value pair. The key and value are separated by a colon :, and each pair is separated by a comma ,.

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my_dict = {'name': 'John', 'age': 30, 'city': 'New York'}

Alternatively, dictionaries can be created using the dict() constructor.

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my_dict = dict(name='John', age=30, city='New York')

‌Accessing Dictionary Elements‌

Elements in a dictionary can be accessed using their key. If the key exists, its value is returned; otherwise, a KeyError is raised.

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print(my_dict['name'])  # Outputs: John

To avoid KeyError, the get() method can be used, which returns None if the key does not exist.

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print(my_dict.get('country'))  # Outputs: None

‌Modifying Dictionaries‌

Dictionaries can be modified by adding new key-value pairs, updating existing ones, or deleting pairs.

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my_dict['country'] = 'USA'  # Adds a new key-value pair
my_dict['age'] = 31  # Updates an existing key's value
del my_dict['city']  # Deletes a key-value pair

‌Dictionary Methods‌

Python dictionaries come with several useful methods for performing common tasks:

• keys(): Returns a view object that displays all the keys in the dictionary.
• values(): Returns a view object that displays all the values in the dictionary.
• items(): Returns a view object that displays a list of dictionary’s (key, value) pair.
• clear(): Removes all items from the dictionary.
• copy(): Returns a shallow copy of the dictionary.
• update(): Updates the dictionary with the specified key-value pairs.
  ‌Looping Through a Dictionary‌

It is common to iterate through a dictionary to access its keys, values, or both.

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# Accessing keys
for key in my_dict.keys():
    print(key)

# Accessing values
for value in my_dict.values():
    print(value)

# Accessing both keys and values
for key, value in my_dict.items():
    print(key, value)

‌Nested Dictionaries‌

Dictionaries can also be nested, meaning a dictionary can be the value of another dictionary’s key. This allows for the creation of complex data structures.

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

Understanding these fundamental aspects of Python dictionaries is crucial for effectively working with data in Python. They provide a flexible way to store and manipulate data, making them an essential tool in any Python programmer’s toolkit.

[tags]
Python, dictionary, data structure, key-value pairs, programming