2 Separating the Code

Let us start by moving the computation functions

Example 1: compute_paint.py

import math


def compute_wall_surface_area(length: float, width: float) -> float:

    area_one_wall = length * width
    area_four_walls = 4 * area_one_wall

    return area_four_walls


def determine_gallons_required(
    wall_area: float, min_coverage: float = 350, max_coverage: float = 400
) -> tuple[int, int]:

    max_gallons = math.ceil(wall_area / min_coverage)
    min_gallons = math.ceil(wall_area / max_coverage)

    return min_gallons, max_gallons

Example 2: estimate_paint.py

from compute_paint import *


def main():
    # Dimensions in feet
    length = 50
    width = 40

    # Price in dollars
    price_per_gallon = 49.95

    area = compute_wall_surface_area(length, width)

    gallons_required = determine_gallons_required(area)

    min_required, max_required = gallons_required
    min_cost = min_required * price_per_gallon
    max_cost = max_required * price_per_gallon

    print(f"You will need to buy {min_required} to {max_required} gallons of paint.")
    print(f"You will spend $ {min_cost:.2f} to $ {max_cost:.2f}")


if __name__ == "__main__":
    main()

Take note of the wildcard import.

from compute_paint import *

These types of imports should always be avoided. The general rule (regardless of language) is import what you need and nothing extra.

Let us import the two functions that we are actually using…

from compute_paint import (compute_wall_surface_area, determine_gallons_required)

3 Renaming the Functions

Since the module (i.e., compute_paint) contains the two functions… their names are a little redundant…

• compute_paint.compute_wall_surface_area
• compute_paint.determine_gallons_required

If we import the module and use the fully qualified function names…

• compute_paint.wall_surface_area
• compute_paint.gallons_required

the module name becomes part of the documentation!

Let us tweak main…

Example 3: estimate_paint.py - Updated Imports

import compute_paint


def main():
    # Dimensions in feet
    length = 50
    width = 40

    # Price in dollars
    price_per_gallon = 49.95

    area = compute_paint.wall_surface_area(length, width)

    gallons_required = compute_paint.gallons_required(area)

    min_required, max_required = gallons_required
    min_cost = min_required * price_per_gallon
    max_cost = max_required * price_per_gallon

    print(f"You will need to buy {min_required} to {max_required} gallons of paint.")
    print(f"You will spend $ {min_cost:.2f} to $ {max_cost:.2f}")


if __name__ == "__main__":
    main()

We can also use tuple unpacking to rewrite…

    gallons_required = compute_paint.gallons_required(area)

    min_required, max_required = gallons_required

as one line…

    min_required, max_required = compute_paint.gallons_required(area)

We should also add the missing period in the second print statement…

    print(f"You will spend $ {min_cost:.2f} to $ {max_cost:.2f}.")

4 Fixing the Output

I do not like the output…

1. There should be a get_report function that returns a str that we then output.

2. There is no logic for the case where the minimum and maximum required gallons of paint are the same

Let us start with where to place the new function… estimate_paint.py. The output logic is program specific. Let us establish the practice of separating computational logic from output (and input) logic.

Example 4: get_report

def get_report(min_gallons: int, max_gallons: int, price_per_gallon: float) -> str:
    min_cost = min_gallons * price_per_gallon
    max_cost = max_gallons * price_per_gallon

    return "\n".join(
        (
            f"You will need to buy {min_gallons} to {max_gallons} gallons of paint.",
            f"You will spend $ {min_cost:.2f} to $ {max_cost:.2f}.",
        )
    )

Take note of the "\n".join((...)). We are taking a tuple of two strings (tuple[str]) and inserting a newline ("\n") between them. The join function comes up quite a bit in Python.

Now… let us add a conditional block to check if min_gallons == max_gallons.

Example 5: get_report - Updated

def get_report(min_gallons: int, max_gallons: int, price_per_gallon: float) -> str:
    if min_gallons == max_gallons:
        gallons = max_gallons
        cost = gallons * price_per_gallon

        return "\n".join(
            (
                f"You will need to buy {gallons} gallons of paint.",
                f"You will spend $ {cost:.2f}.",
            )
        )

    else:
        min_cost = min_gallons * price_per_gallon
        max_cost = max_gallons * price_per_gallon

        return "\n".join(
            (
                f"You will need to buy {min_gallons} to {max_gallons} gallons of paint.",
                f"You will spend $ {min_cost:.2f} to $ {max_cost:.2f}.",
            )
        )

5 Done… for the Moment

For the moment… let us consider this example complete. We will revisit it in a few modules for a code review discussion.