Script to figure out how much a contract on Upwork must pay to come out to a certain real total for the freelancer

calculate_payment.py

from itertools import chain, repeat

def is_floatable(num):
    try:
        float(num)
        return True
    except ValueError:
        return False

# based on this glorious StackOverflow post: https://stackoverflow.com/a/56081775
def number_input(
    prompt="Enter a number: ", 
    error="Not a number! Try again: "):

    prompts = chain([prompt], repeat(error))
    replies = map(lambda i: int(input(i)), prompts)
    valid_response = next(filter(is_floatable, replies))
    return valid_response

# money you want to actually receive on the current contract
desired_income_USD = number_input(
    'How much money to you want to make after fees: ')

# money the client has already paid you on previous contracts
# (how much the client PAID, not how much you RECEIVED after service fees!)
amount_already_paid_from_same_client_USD = number_input(
    'How much money has the client paid you (not counting fees): ')

T = desired_income_USD
A = amount_already_paid_from_same_client_USD
# for a desired final income of $T, with a client who has already paid you $A
max_80_pct = min(500, (max(T - A, 0) / .8))
print(max_80_pct)
real_T = max_80_pct + (T - (max_80_pct * .8)) / .9
print(f'You must charge $%.2f to make a total of ${T} for a client who has already paid you ${A} (of which $%.2f will go to fees)' % (real_T, real_T - T))