fv + pv*(1+rate)**nper + pmt*(1 + rate*when)/rate*((1 + rate)**nper – 1) == 0 

or when rate == 0
fv + pv + pmt * nper == 0 

# Python program explaining 
# ipmt() function 
  
import numpy as np 
''' 
Question : 
  
monthly payment needed to pay off a $10, 000 loan
in 12 years at an annual interest rate of 60 %
'''
  
Solution = np.ipmt(0.6 / 12, 2 * 12, 1 * 12, 10000)
  
# Here fv = 0 ; Also Default value of fv = 0 
print("Solution - ipmt value : ", Solution) 

Solution - ipmt value :  801.4432933339593