input: Write a python function to calculate the monthly mortgage payment.
  assert abs(monthly_mortgage_payment(100000, 0.05, 30) - 536.82) < 0.01
  assert abs(monthly_mortgage_payment(200000, 0.04, 20) - 1212.44) < 0.01
  assert abs(monthly_mortgage_payment(150000, 0.03, 15) - 1035.56) < 0.01
output: def monthly_mortgage_payment(principal, annual_rate, years):
      monthly_rate = annual_rate / 12
      number_of_payments = years * 12
      monthly_payment = principal * (monthly_rate * (1 + monthly_rate) ** number_of_payments) / ((1 + monthly_rate) ** number_of_payments - 1)
      return monthly_payment