root/hodgestar/PythonCode/SmallScripts/bond.py

import sys

def Usage(aArgs):
    print "usage:", aArgs[0], "<bond amount>", "<months>", "<rate>"
    print "  Outputs monthly repayments."
    print "  <bond amount> in some currency."
    print "  <months> over which loan will be repayed."
    print "  <rate> as an annual percentage which is compounded monthly."

def Main(aArgs):
    if len(aArgs) != 4:
        Usage(aArgs)
        return 1

    X = float(aArgs[1])
    M = int(aArgs[2])
    r = float(aArgs[3])
    
    q = r/(100.0*12.0)
    p = 1.0 + q
    
    Z = [p**n for n in range(0,M+1)]
    D = X * Z[M] / sum(Z[0:M]) # Repayments
    
    An = [X*Z[n] - D*sum(Z[0:n]) for n in range(0,M+1)] # Amounts owed
    Rn = [An[n] - An[n+1] for n in range(0,M)]
    
    print "Repayments:", D
    print "Amounts:"
    print "\n".join([str(x) + " : " + str(An[x]) for x in range(0,M,24)])
    print "Reductions:"
    print "\n".join([str(x) + " : " + str(Rn[x]) for x in range(0,M,24)])
    return 0

if __name__ == "__main__":
  sys.exit(Main(sys.argv))