5.3. Data Structures in Python: Dictionaries

Python dictionaries are an invaluable and powerful data structure that every programmer should know. They are a fundamental part of Python and are used in a variety of applications. In this section of our e-book course, we will discuss Python dictionaries in detail.

A dictionary in Python is an unordered collection of items. While other composite data types only have a value as an element, a dictionary has a key:value pair. The "Python" key and value are separated by a colon, and the set of key:value pairs is wrapped in curly braces {}. For example:

my_dictionary = {
    "key1": "value1",
    "key2": "value2",
    "key3": "value3"
}

A dictionary key can be of any immutable type, such as a string, a number, or a tuple. The values ​​of a dictionary can be of any type and can be modified, which means that a dictionary is a mutable data structure.

Dictionaries are optimized to retrieve values ​​when the key is known. This is possible due to the fact that dictionaries in Python are implemented as hash tables.

To access the value of a specific key, you can use the following syntax:

print(my_dictionary["key1"]) # Output: value1

If you try to access a key that doesn't exist in the dictionary, Python will throw an error. To avoid this, you can use the get() method, which returns None if the key doesn't exist:

print(my_dictionary.get("nonexistent_key")) # Output: None

To add a new key:value pair to the dictionary, you can use the following syntax:

my_dictionary["key4"] = "value4"
print(my_dictionary) # Output: {'key1': 'value1', 'key2': 'value2', 'key3': 'value3', 'key4': 'value4'}

To remove a key:value pair from a dictionary, you can use the keyword del:

from my_dictionary["key1"]
print(my_dictionary) # Output: {'key2': 'value2', 'key3': 'value3', 'key4': 'value4'}

In addition, Python dictionaries have a variety of useful methods. For example, the keys() method returns a new view of the keys dictionaries. Similarly, the values() method returns a new view of all the values ​​in the dictionary.

print(my_dictionary.keys()) # Output: dict_keys(['key2', 'key3', 'key4'])
print(my_dictionary.values()) # Output: dict_values(['value2', 'value3', 'value4'])

In conclusion, Python dictionaries are a powerful and versatile tool. They allow you to efficiently store and retrieve values ​​and are fundamental to many aspects of Python programming. Whether you're a beginner or an experienced programmer, understanding dictionaries is essential to writing effective and efficient Python code.

In the next chapter of this e-book course, we'll explore data structures in Python even further, focusing on lists and tuples. Stay tuned!