Summary  
This chapter covers how to define and use variables to store data, perform arithmetic operations on them, and display results via printing.

General domain of usage  
Retail inventory management

Mastering variables **isn't just about storing data** — it's also about using this data to perform meaningful operations. Variables allow you to **calculate and manipulate data**, enabling you to handle tasks such as pricing adjustments or inventory management in your programs.

Let's see how Alex uses variables that store different data types:

First, let's see how we can use variables to **calculate the total cost of items**. This example multiplies the **price per unit** by the quantity to determine how much it would cost to buy a certain number of items:

# Calculate the total cost of 100 cupcakes
item_price = 0.50
item_quantity = 100
total_cost = item_price * item_quantity

print("Total cost for", item_quantity, "cupcakes is $", total_cost)

You can't use a variable before assigning a value to it. If you try to access a variable that hasn't been assigned, Python will raise a `NameError`. Always make sure to assign a value to your variable before you use it in calculations or print statements.

Note

import unittest
import importlib
from io import StringIO
from contextlib import redirect_stdout
import re

import user_code


def _dynamic_test(test_case, condition, success_message, failure_message):
    if condition:
        test_case._testMethodName = success_message
        test_case.assertTrue(True, success_message)
    else:
        test_case._testMethodName = failure_message
        test_case.fail(failure_message)


class TestUserCode(unittest.TestCase):
    def normalize_text(self, text):
        text = text.lower()
        text = re.sub(r'\s*:\s*', ':', text)
        text = re.sub(r'\s+', ' ', text)
        return text.strip()

    def test_item_name_declared_and_correct(self):
        _dynamic_test(
            self,
            hasattr(user_code, 'item_name') and user_code.item_name == "Soda",
            'item_name is declared and equals "Soda"',
            f'Expected item_name to be "Soda", but got "{getattr(user_code, "item_name", None)}".'
        )

    def test_item_price_declared_and_correct(self):
        _dynamic_test(
            self,
            hasattr(user_code, 'item_price') and isinstance(user_code.item_price, float) and user_code.item_price == 6.99,
            'item_price is declared and equals 6.99',
            f'Expected item_price to be 6.99, but got {getattr(user_code, "item_price", None)}.'
        )

    def test_purchase_quantity_declared_and_correct(self):
        _dynamic_test(
            self,
            hasattr(user_code, 'purchase_quantity') and isinstance(user_code.purchase_quantity, int) and user_code.purchase_quantity == 5,
            'purchase_quantity is declared and equals 5',
            f'Expected purchase_quantity to be 5, but got {getattr(user_code, "purchase_quantity", None)}.'
        )

    def test_total_cost_declared_and_correct(self):
        expected = 6.99 * 5
        _dynamic_test(
            self,
            hasattr(user_code, 'total_cost') and isinstance(user_code.total_cost, float) and round(user_code.total_cost, 2) == round(expected, 2),
            'total_cost is declared and calculated correctly',
            f'Expected total_cost to be {expected}, but got {getattr(user_code, "total_cost", None)}.'
        )


if __name__ == '__main__':
    unittest.main()

test_main.py

Python is a high-level, interpreted, general-purpose programming
language. Distinguished from languages such as HTML, CSS, and JavaScript, which are mainly
utilized in web development, Python boasts versatility across multiple domains, including
software development, data science, and back-end development. This course will guide you
through Python's fundamental concepts, equipping you with the skills to create your own
functions by the conclusion of the program.

In this section, you will explore the fundamentals of Python, get acquainted
with your workspace, perform simple math operations, and display your findings.

In this section, you'll discover how to save items such as numbers and text
in computer memory and retrieve them by name. Additionally, you'll gain an introduction to text
manipulation in Python.

In this section, you'll explore the boolean data type and learn how it is used
to develop programs that react to certain conditions.

In this section, you will continue learning about data types and discover
how to organize various attributes in a single variable using lists, tuples, and dictionaries.

In this section, you'll learn how to create loops in Python — an essential skill
for iterating through lists, tuples, and dictionaries.

To conclude this introductory course, you will explore some built-in
functions and then begin to develop your own!

Which of these is a correct way to create a variable?

Given the string `"Banana"`, which code retrieves its first character?

What will be the output of the following code?

Using Variables

Code Instructions

解答