Python Diaries ….. Day 6

Dictionaries…

4 min readSep 18, 2023

Today’s class is all about a versatile and powerful data structure: dictionaries. Dictionaries in Python allow us to store data in key-value pairs, providing a fast and efficient way to retrieve information based on unique keys. They are often likened to real-world dictionaries, where you look up a word (the key) to find its definition (the value).

In this class, we’ll explore how to create, manipulate, and leverage dictionaries in Python. Get ready to unlock a new level of data organization and retrieval! Let’s get started!

Creating a Dictionary

Dictionaries are created using curly braces {} and consist of key-value pairs separated by colons :

# Example of a dictionary
person = {
    "name": "John Doe",
    "age": 30,
    "city": "New York"
}
# output will be {'name': 'John Doe', 'age': 30, 'city': 'New York'}py

In this example, "name", "age", and "city" are the keys, each associated with a respective value.

A dictionary is a collection which is ordered*, changeable and do not allow duplicates.

# Example of a dictionary
person = {
    "name": "John Doe",
    "age": 30,
    "city": "New York",
    "city": "Washington"
}
# output will be {'name': 'John Doe', 'age': 30, 'city': 'Washington'}

Accessing Values

You can access the value of a specific key using square brackets [] and the key itself.

person = {
    "name": "John Doe",
    "age": 30,
    "city": "New York"
}

# Accessing values
name = person["name"]  # Output: "John Doe"
age = person["age"]    # Output: 30

You can also use get() function to get the values.

name = person.get("name")

Modifying Dictionaries

Dictionaries are mutable, which means you can change the values associated with keys.

# Modifying values
person["age"] = 31

# using update function
person.update({"age":45})

Adding New Entries

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

# Adding a new entry
person["email"] = "john.doe@example.com"

Dictionary Methods

Dictionaries come with a variety of built-in methods for performing operations. Some commonly used methods include keys(), values(), and items().

# Getting keys, values, and items
keys = person.keys()      # Output: dict_keys(['name', 'age', 'city', 'email'])
values = person.values()  # Output: dict_values(['John Doe', 31, 'New York', 'john.doe@example.com'])
items = person.items()    # Output: dict_items([('name', 'John Doe'), ('age', 31), ('city', 'New York'), ('email', 'john.doe@example.com')])

Removing Entries

You can remove a key-value pair from a dictionary using the pop() ,popitem() ,clear() and del method.

# Removing an entry using pop()
city = person.pop("city")  # city is "New York", person no longer contains "city" key

# Removing an entry using popitem()
key, value = person.popitem()  # Removes and returns the last key-value pair (key = 'city', value = 'New York')# Removing an entry using clear()
person.clear()  # Removes all items from 'person' (person is now an empty dictionary)# Removing an entry using clear()
del person["age"], person["city"]  # Removes both 'age' and 'city' keys and their associated values

Sorting a Dictionary

Dictionaries are inherently unordered, but you can sort them based on keys or values if needed. To sort a dictionary, you can use the sorted() function with a key argument.

Sorting by Keys:

person = {
    "name": "John Doe",
    "age": 30,
    "city": "New York"
}

sorted_dict_by_keys = dict(sorted(person.items()))
print(sorted_dict_by_keys)

Sorting by Values:

person = {
    "name": "John Doe",
    "age": 30,
    "city": "New York"
}

sorted_dict_by_values = dict(sorted(person.items(), key=lambda item: item[1]))
print(sorted_dict_by_values)

Loop Through a Dictionary

Looping through a dictionary allows you to access its keys and values for various operations. There are several methods to achieve this:

Looping Through Keys: You can loop through the keys of a dictionary using a for loop.

person = {
    "name": "John Doe",
    "age": 30,
    "city": "New York"
}

for key in person:
    print(key)

Looping Through Values: You can loop through the values of a dictionary using the values() method.

person = {
    "name": "John Doe",
    "age": 30,
    "city": "New York"
}

for value in person.values():
    print(value)

Looping Through Both Keys and Values: You can loop through both the keys and values simultaneously using the items() method.

person = {
    "name": "John Doe",
    "age": 30,
    "city": "New York"
}

for key, value in person.items():
    print(f"{key}: {value}")

Nested Dictionaries

A nested dictionary is a dictionary that contains other dictionaries as its values. This allows for more complex data structures.

students = {
    "student1": {
        "name": "John Doe",
        "age": 20,
        "major": "Computer Science"
    },
    "student2": {
        "name": "Jane Doe",
        "age": 21,
        "major": "Mathematics"
    }
}

You can access values in a nested dictionary by chaining the keys:

print(students["student1"]["name"])  # Output: John Doe

Dictionaries are a fundamental data structure in Python, providing an efficient way to organize and access data using unique keys. With their flexibility and versatility, dictionaries play a crucial role in a wide range of Python applications.

You can access the other topics in this tutorial series right here:

In Day 7, we’ll explore condition statements in python. Keep up the great work! Happy coding!