Hello, everyone!
I’m just about half way through LPTHW (version 3), and I’m really enjoying my progress so far. I think I remember hearing Zed say in one of the half-way point videos that “I now know enough to write some really terrible python programs”. He’s right!
I took a little break because I’m in the middle of buying a new car, and thought I could use Python to help me figure out my new monthly car payment. The following little program takes values related to the new car purchase (price/apr/terms of loan), and then returns the monthly payment:
print("""
Welcome to the payment calculator!
Based on the info you enter, we will
show you the amount of your monthly auto
loan payment. Enter only whole numbers, and
do not use any symbols (e.g., $ or %).\n
Let's get started!
""")
amount = float(input("Enter the negotiated price of you new car: $ "))
trade_in = float(input("Enter the amount of any trade-in vehcile (enter 0 if none): $ "))
tax = float(input("Enter the sales tax rate for your state: % "))
apr = float(input("Enter the APR rate: % "))
term = float(input("Enter the number of years you wish to finance: "))
print("\nHere's what you entered:\n")
print(f"Negotiated price: ${amount}")
print(f"Trade-in value: ${trade_in}")
print(f"Sales tax: {tax}%")
print(f"APR: {apr}%")
print(f"Term: {term} years")
def net_trade_in(new_car, old_car):
tradein = new_car - old_car
return tradein
def tax_rate(value, state_rate):
tax_value = state_rate / 100
states_taxes = tax_value * value
return states_taxes
def apr_rate(bottom_line, apr_rate):
apr_value = apr_rate / 100
apr_taxes = apr_value * bottom_line
return apr_taxes
def year_terms(bottom_bottom_line, total_years):
how_many_months = total_years * 12
monthly_payment = bottom_bottom_line / how_many_months
return monthly_payment
tradein_balance = net_trade_in(amount, trade_in)
state_taxes_hurt = tax_rate(tradein_balance, tax) + tradein_balance
apr_also_hurt = apr_rate(state_taxes_hurt, apr) + state_taxes_hurt
monthly_pain = year_terms(apr_also_hurt, term)
print(f"\nNet trade-in balance: ${tradein_balance}")
print(f"Total amount after taxes: ${state_taxes_hurt}")
print(f"Total amount after apr: ${apr_also_hurt}")
print(f"\nMonthly payment: ${monthly_pain}\n")It’s really easy to break things, so only use whole numbers, no commas, and no symbols ($ or %) at the prompts. I think I got the math right, at least it worked for me and matches what I see for my recent new car purchase.
What really helped me was going REALLY SLOW – especially on each of the functions. And use “print” a lot to find out what’s happening along the way.
Anyway, like I said, it’s a really terrible program, and I’m sure there way better ways to do this, but it’s got me motivated to move forward and finish the book!
