Python Dictionaries: Dynamic Data Structures

What are Dictionaries?

Python dictionaries are a fundamental data structure used to store and manage collections of data in a way that allows for efficient retrieval and modification. Dictionaries are also known as associative arrays or hash maps in other programming languages.

Here are the key aspects of Python dictionaries you should know:

Definition:

A dictionary in Python is defined using curly braces {} or the dict() constructor. It consists of key-value pairs, where each key is unique and associated with a value. The key is used to look up the corresponding value.

# Creating an empty dictionary
my_dict = {}

# Creating a dictionary with key-value pairs
student = {
    "name": "Alice",
    "age": 25,
    "grade": "A"
}

Accessing Values:

You can access the values in a dictionary using square brackets [] and providing the key.

print(student["name"])  # Output: "Alice"
print(student["age"])   # Output: 25

Modifying Values:

You can change the value associated with a key in a dictionary by assigning a new value to it.

student["age"] = 26

Adding New Key-Value Pairs:

You can add new key-value pairs to a dictionary by simply assigning a value to a new key.

student["city"] = "New York"

Removing Key-Value Pairs:

You can remove a key-value pair from a dictionary using the del keyword or the pop() method.

del student["grade"] # Deletes the "grade" key and its value
popped_value = student.pop("city") # Removes the "city" key and returns its value

Checking for Key Existence:

You can check if a key exists in a dictionary using the in keyword.

if "name" in student:
    print("Name exists in the dictionary")

Iterating Over a Dictionary:

You can loop through the keys, values, or key-value pairs in a dictionary using for loops.

for key in student:
    print(key, student[key])

# Using items() to iterate through key-value pairs
for key, value in student.items():
    print(key, value)

Dictionary Methods:

Python dictionaries come with several useful methods such as keys(), values(), items(), get(), clear(), copy(), and more. These methods help you manipulate and work with dictionaries efficiently.

keys_list = student.keys()   # Returns a list of keys
values_list = student.values()  # Returns a list of values

Dictionary Comprehensions:

You can create dictionaries using dictionary comprehensions, which are similar to list comprehensions but for dictionaries.

squares = {x: x*x for x in range(1, 6)}
# Output: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}