Sales Tax Calculator in Python

Table of Contents

1. Challenge

   Step 1: Explore the Project and the Learning Path

   This lab turns a few lines of Python shell math into a small, reusable sales tax calculator program. The shell is great for quick experiments because it echoes values automatically. Scripts are what you keep, rerun, and share.

   To stay organized, this project splits responsibilities across a few files:

   • app/calculator.py — defaults and tax math
   • app/formatting.py — currency and summary output
   • app/io_helpers.py — input parsing and prompts
   • app/workflows.py — demo workflow
   • tax.py — script entry point

   The starter code includes tests for each task. Work through the tasks in order and run the check when you finish one. > If you get stuck, you can refer to the provided solution code for each task, available in the solution folder. info> This lab experience was developed by the Pluralsight team using an internally developed AI tool. All sections were verified by human experts for accuracy prior to publications. However, content may still contain errors or inaccuracies, and we recommend independent verification.
   
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2. Challenge

   Step 2: Recreate the Shell Math in Reusable Calculator Functions

   This step builds the mathematical core in app/calculator.py. In the shell, one expression like amount + amount * tax is enough. In a script, it helps to name the pieces: defaults at the module level, a helper for tax only, and a helper for the full total. That separation makes the code easier to test and reuse. A common starting point is amount = 10 and tax = 0.06. In a script, those values belong in one clear place so the rest of the code can reuse them. Python often uses uppercase names such as DEFAULT_AMOUNT to signal stable default values. Next, pull the tax calculation into its own helper. The expression amount * tax becomes a function that returns only the tax portion, not the full total. The full formula is total = amount + amount * tax. Instead of repeating the multiplication, call calculate_tax() from calculate_total() so each function has one clear job.

3. Challenge

   Step 3: Turn Raw Numbers Into Readable Script Output

   The shell shows a value when you type a variable name, but a saved script does not display anything unless you print it. This step adds formatting helpers and connects them to the script. Raw floats like 10.6 are not ideal for users. An f-string with a .2f format specifier can turn that into currency text such as $10.60. A single formatted number is not enough for a useful script. Build a multi-line summary that explains the amount, tax rate, and total, then return that string so other parts of the app can print or test it. Now connect the default calculator values to visible output. Build the summary first, then pass it to output_func so the script produces console output when it runs.

4. Challenge

   Step 4: Accept New Values Through Text Input

   Changing values still means editing code unless the program can read input. User input arrives as text, so you need parsing and validation before the calculator can use the values. Start with the purchase amount. Strip whitespace, convert with float(), and reject invalid or negative values with ValueError. Tax rates are trickier because users may enter 0.06, 7, or 7%. Normalize those forms into one decimal rate the calculator can use, such as 0.07. With the parsers in place, wire up a small interactive workflow: prompt for both values, parse them, build the summary, and print the result.

5. Challenge

   Step 5: Finish Reusable Workflows and the Script Entry Point

   The final step adds application flow. A demo workflow can show both example calculations in sequence, and main() gives the script one clear entry point. Start with one default calculation and then a rerun with new values. Package both examples into one reusable demo function instead of editing variables each time. Finish by routing execution through main(). The if __name__ == '__main__': guard keeps imports safe, while main() decides whether to run the default, demo, or prompt workflow. Run python tax.py to see the finished calculator. You now have reusable math helpers, readable output, input parsing, and a clean script entry point.