How to round this code without getting an error?

[wlsa]

I first used the following code

balance=42
annualInterestRate=.2
monthlyPaymentRate=0.04


month=1
while month <=12:
    balance=(balance+balance*(annualInterestRate/12))-(monthlyPaymentRate*(balance+balance*(annualInterestRate/12)))
    print('Month ' +str(month) + ' Remaining balance: '+ str(balance)
    month+=1

I then realized I want the balance in line 9 to round to 2 decimal places so I edited my code to

balance=42
annualInterestRate=.2
monthlyPaymentRate=0.04


month=1
while month <=12:
    balance=(balance+balance*(annualInterestRate/12))-(monthlyPaymentRate*(balance+balance*(annualInterestRate/12)))
    print('Month ' +str(month) + ' Remaining balance: '+ str(round(balance, 2))
    month+=1

Note line 9, the only thing I changed was to print the balance as rounded.
Python is giving me an error when I try the second posted code, what is wrong with it??

[ichabod801]

Please post the full text of the error you are getting.

[ljmetzger]

Please note that both your examples do not run. They both need an extra ) at the end of the print statement (line 9) to run.

After correcting the error, your code works, but does not print two decimal places in all instances (output excerpt follows):

Output:
Month 4 Remaining balance: 38.11
Month 5 Remaining balance: 37.2
Month 6 Remaining balance: 36.3
Month 7 Remaining balance: 35.43

Try the following new format line:

balance = 42
annualInterestRate = .2
monthlyPaymentRate = 0.04
 
month = 1
while month <= 12:
    balance = (balance + balance * (annualInterestRate/12)) - (monthlyPaymentRate * (balance + balance * (annualInterestRate / 12)))
    print('Month {:2}     Remaining balance: {:.2f}'.format(month, balance))
    month += 1

Output:
Month  1     Remaining balance: 40.99
Month  2     Remaining balance: 40.01
Month  3     Remaining balance: 39.05
Month  4     Remaining balance: 38.11
Month  5     Remaining balance: 37.20
Month  6     Remaining balance: 36.30
Month  7     Remaining balance: 35.43
Month  8     Remaining balance: 34.58
Month  9     Remaining balance: 33.75
Month 10     Remaining balance: 32.94
Month 11     Remaining balance: 32.15
Month 12     Remaining balance: 31.38

Now a couple of recommendations to improve your code and make it more pythonic:
a. Python variable names are recommended to be all lower case (e.g. annualInterestRate should be annual_interest_rate).
b. Spaces are recommended before and after operators month += 1.
c. A for loop is usually preferred to a while loop.
d. Rearranging and simplifying your balance equation
For future reference, Python coding rules (and recommendations) are in PEP-8. See https://www.python.org/dev/peps/pep-0008/

balance = 42
annualInterestRate = .2
monthlyPaymentRate = 0.04
 
#NOTE: range(1, 13) executes 1 thru 12
for month in range(1, 13):
    balance = (balance + balance * (annualInterestRate/12)) * (1.0 - monthlyPaymentRate)
    print('Month {:2}     Remaining balance: {:.2f}'.format(month, balance))

Lewis