[Tutor] How to refactor a simple, straightforward script into a "proper" program?

[boB Stepp]

I now believe that I have a finalized version2.py that I am satisfied
with.  I have not done the optional type annotations and am in
progress adding tests.  I may have some questions about the resulting
tests once I complete them.  But for my New Year's Python 3 exercise,
I wish to throw out the below code for code review by anyone who
wishes to assist boB on his ongoing learning journey.  Let me know of
*anything* that you think I should have done better or more
professionally or in a more Pythonic style, etc.

Another goal I had hoped to accomplish, but have apparently failed at,
was to draw in fellow Python learners into the discussion.  So many
times we are asked on this list what can we do to learn how to program
in Python, and the oft-recommended advice is to come up with a project
and code it, asking for help as necessary.  I thought showing a simple
program and working on improving it might be helpful for other
learners.  Of course the end result to this point has grown from an
original 23 LOC to 97 LOC (including blank lines), so have I really
improved the original product?  I await the scores from the judges!

<final version2.py>
============================================================================
#!/usr/bin/env python3
"""Calculate the number of pages per day needed to read a book by a
given date."""

from datetime import date


def get_input(str_converter, msg):
    """Prompt user with a message and return user input with the
correct data type."""
    while True:
        try:
            return str_converter(input(msg))
        except ValueError:
            if str_converter == int:
                print("\nPlease enter a whole number!")
            elif str_converter == date.fromisoformat:
                print("\nPlease enter a valid date in the following
format yyyy-mm-dd!")


def get_input_params():
    """Collect all needed input parameters."""
    while True:
        str_converters = [int, int, date.fromisoformat]
        input_msgs = [
            "How many pages are there in your book?  ",
            "How many pages have you read?  ",
            "What is your date to finish the book (yyyy-mm-dd)?  ",
        ]
        num_pages_in_book, num_pages_read, goal_date = map(
            get_input, str_converters, input_msgs
        )
        input_params = num_pages_in_book, num_pages_read, goal_date
        if validate_input_params(*input_params):
            return input_params
        print()


def validate_input_params(num_pages_in_book, num_pages_read, goal_date):
    """Verify input parameters for logical correctness."""
    valid_input = True
    print()
    if num_pages_in_book <= 0:
        print("The number of pages in a book must be a positive integer!")
        valid_input = False
    if num_pages_read < 0:
        print("The number of pages read must be a whole number!")
        valid_input = False
    if num_pages_read == num_pages_in_book and num_pages_in_book > 0:
        print(
            "You have already read the entire book!  Why are you
running this program?"
        )
    if num_pages_read > num_pages_in_book:
        print("You cannot have read more pages than there are in the book!")
        valid_input = False
    if goal_date < date.today():
        print("You cannot set a goal date in the past!")
        valid_input = False
    return valid_input


def calc_pages_per_day(num_pages_in_book, num_pages_read, goal_date):
    """Return number of pages to read each day to attain goal."""
    COUNT_TODAY = 1
    days_to_goal = (goal_date - date.today()).days
    pages_per_day = (num_pages_in_book - num_pages_read) /
(days_to_goal + COUNT_TODAY)
    return pages_per_day


def display_result(pages_per_day):
    """Display how many pages per day the reader must read to finish
the book."""
    if 0 < pages_per_day <= 1:
        word_to_display = "page"
    else:
        word_to_display = "pages"
    print(
        "You must read {0:.2n} {1} per day to reach your goal.".format(
            pages_per_day, word_to_display
        )
    )


def main():
    """Run program and display results."""
    print(
        'Welcome to "HOW MANY PAGES???"\n'
        "Follow on-screen directions to determine how many pages to
read each day to "
        "finish your book.\n\n"
    )
    while True:
        input_params = get_input_params()
        display_result(calc_pages_per_day(*input_params))
        run_again = input("Enter 'q' to quit or anything else to continue:  ")
        if run_again.lower().startswith("q"):
            break


if __name__ == "__main__":
    main()
============================================================================

boB