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Python beginner - BigDisAok - Jun-23-2018
Hi all,
I am new to Python (really enjoying it so far) and am working my way through Learn Python the hard way. I have just learnt about functions and decided to go off piste and make myself a question to solve. I can't find the answer online, so was wondering if you good people can help me.
Problem PART A : I am trying to work out how much of my mortgage is left after X months of repayment. In this case, amount borrowed - 200000, Interest rate 0.03 per anum, time: 72 months, paying back 750 a month:
def mortgage(borrowed, repayment, interest, time):
print(f"total left after {time} months \n")
print(borrowed * (interest/12 +1)-repayment) #this calculates mortgage left after 1 month. How do I repeat this calculation on the answer? 71 times
mortgage(200000,750,.03,72)Many Thanks,BigD :)
RE: Python beginner - Nwb - Jun-23-2018
months*(borrowed * (interest/12 +1)-repayment))?
RE: Python beginner - BigDisAok - Jun-23-2018
(Jun-23-2018, 11:57 AM)Nwb Wrote: months*(borrowed * (interest/12 +1)-repayment))?
that does not work, because after 1 month the amount owed has reduced and thus the interest owed is less.
RE: Python beginner - gontajones - Jun-23-2018
Just check if the repayment has to be after or before the interest calculation.
def mortgage(borrowed, repayment, interest, time):
print(f"total left after {time} months \n")
for m in range(time):
borrowed = borrowed - repayment
borrowed = borrowed * (1 + interest / 12)
print(borrowed)
mortgage(200000, 750, .03, 72)
RE: Python beginner - BigDisAok - Jun-23-2018
repayment is subtracted after interest has been added.
RE: Python beginner - gontajones - Jun-23-2018
So...
def mortgage(borrowed, repayment, interest, time):
print(f"total left after {time} months \n")
while (time > 0):
borrowed = borrowed * (1 + interest / 12)
borrowed = borrowed - repayment
time -= 1
print(borrowed)
mortgage(200000, 750, .03, 72)It's not necessary to use a for loop.
RE: Python beginner - Grok_It - Jun-24-2018
(Jun-23-2018, 01:21 PM)gontajones Wrote: So...
def mortgage(borrowed, repayment, interest, time): print(f"total left after {time} months \n") while (time > 0): borrowed = borrowed * (1 + interest / 12) borrowed = borrowed - repayment time -= 1 print(borrowed) mortgage(200000, 750, .03, 72)It's not necessary to use a for loop.
Why on earth would you eliminate a range count in favor of a while loop?
Each iteration of a range count takes 3 operations, the equivalent in a while loop takes 10 operations, assuming all internal operations are amalgamated as one.
range is implemented completely in c, while and "time -= 1" are interpreted commands and are very slow comparatively.
RE: Python beginner - gontajones - Jun-24-2018
Quote:Why on earth would you eliminate a range count in favor of a while loop?Just to be clearer.
RE: Python beginner - Grok_It - Jun-24-2018
(Jun-24-2018, 05:08 PM)gontajones Wrote:Quote:Why on earth would you eliminate a range count in favor of a while loop?Just to be clearer.
for month in range(months):
borrowed *= 1 + interest / 12
borrowed -= repayment
print(borrowed)With a little cleaning and some proper variable names the for loop is perfectly clear, but I do respect wanting to clean up code. I like my code neat too, but never at the cost of speed. Try it for yourself. Run both for 100K months.
RE: Python beginner - gontajones - Jun-24-2018
Quote: for month in range(months):
borrowed -= repayment
borrowed *= (1 + interest / 12)
print(borrowed)With a little cleaning and some proper variable names the for loop is perfectly clear, but I do respect wanting to clean up code. I like my code neat too, but never at the cost of speed. Try it for yourself. Run both for 100K months.
I completely agree with you. But maybe a beginner would read this and ask why the 'month' ('m' in my case) variable exists.