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Python function for calculating compound interest percentage

I'm new to programming, so any experienced programmer will probably be able to answer this question easily.
I am trying to write a Python function which will tell me what percentage compound interest is necessary to end up with a specific sum. For example, if I deposited $100, and after 17 years of compound interest I have $155, the function will tell me what percentage interest was I receiving. I wrote the following function, with 'start' being the original sum deposited, 'finish' the sum I ended up with, and 'years' the number of years it accrued interest. I designed it to give a result in decimal points, for example for 1.5% it will show 0.015.
Here's the code I wrote:
def calculate(start, finish, years):
num = start
percentage = 0
while num < finish:
percentage += 0.000001
for year in range(years):
num += num * percentage
return percentage
print(calculate(12000, 55000, 100))
It's giving an output of 0.00017499999999999962 (i.e. 0.017499999999999962%), which is totally wrong.
I can't understand where I've gone wrong.

You need to reset the num=start after every time you guess a percentage.
def calculate(start, finish, years):
num = start
percentage = 0
while num < finish:
num = start
percentage += 0.000001
for year in range(years):
num += num * percentage
return percentage
print(calculate(12000, 55000, 100))
However, you'd probably be better off solving this problem by simply re-arranging the compound interest formula:
A=P*(1+r/n)^(nt)
(where A = Final balance, P = Initial balance, r = Interest rate, n = number of times interest applied per time period, and t = number of time periods elapsed.)
The rearrangement gives:
r=n((A/P)^(1/nt)-1)
and putting this into python gives us:
def calculate(start, finish, years):
num = ((finish / start)**(1/years))-1
return num
print(calculate(12000.0, 55000.0, 100.0))
which gives the expected results.

You can do a one-liner if you understand how compound interest works
def calculate(start, finish, years):
return (finish/start)**(1/years) - 1
print(calculate(12000, 55000, 100) * 100, '%')

Loop code with: {x_(n+1) = x_n * r * (1- x_n)}

Little new here and any help would be appreciated.
I have been tooling around with this code for a while now and I cant seem to wrap my head around it. Im fairly new to python so I dont quite know or remember all the tricks yet/skills.
So the question at hand:
Equation: {x_(n+1) = x_n * r * (1- x_n)}
With x_n between (0,1) and r between (0,4).
The goal here is to make a loop function that will gather a value for 'x_n' and 'r' and spit out the iteration 'n' and the current 'x_n+1'; i.e. print(n , x_n+1), at each 'n' step while checking to see if the new value is within 0.0000001 of the old value.
If it settles on a fixed point within 20,000 (0.0000001), print the final 'n' + message. If not then and goes to 20,000 then print another message.
All i have so far is:
import math
x_o=float(input("Enter a 'seed' value: "))
r=float(input("Enter an 'r' value: "))
x_a=((x_o + 0) * r * (1-(x_o + 0)))
while x_a != (0.0000001, x_o , 0.0000001):
for n in range(0,99):
x_a=((x_o + n) * r * (1-(x_o + n)))
print(n , x_a)
I'm pretty sure this is no where close so any help would be awesome; if you need any more info let me know.
Much appreciated,
Genosphere

You could write a generator function and use it directly in your for loop. If you need to keep track of the rank of intermediate values you can use enumerate on the generator.
def fnIter(fn,x,delta=0.000001):
while True:
yield x
prev,x = x,fn(x)
if abs(x-prev)<delta:break
output:
r = 2
seed = 0.1
for i,Xn in enumerate(fnIter(lambda x:x*r*(1-x),seed)):
print(i,Xn)
0 0.1
1 0.18000000000000002
2 0.2952
3 0.41611392
4 0.4859262511644672
5 0.49960385918742867
6 0.49999968614491325
7 0.49999999999980305
To implement the maximum iteration check you can either add a conditional break in the loop or use zip with a range:
maxCount = 20000
n,Xn = max(zip(range(maxCount+1),fnIter(lambda x:x*r*(1-x),seed)))
if n < maxCount:
print(n,Xn)
else:
print(Xn,"not converging")

This is an exponentially-weighted moving average. Pandas has a function for this: https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.ewm.html

You have a good start so far. You might be overthinking it, though.
The following approach just tries to generate this sequence for 20,000 terms. Each time, it checks whether the new value is within 0.0000001 from the previous value. If so, it breaks out of the loop and prints that. If not, it uses python's for/else construct to print a different value. Note the different levels of indentation.
x_0 = float(input("enter a 'seed' value: "))
r = float(input("enter an 'r' value: "))
x_m = x_0 # placeholder for 'previous value'
delta = 0.0000001
# Try to calculate 20 thousand terms of this sequence
# We will break out of the loop early if our x_n converges
for _ in range(20000):
x_n = x_m * r * (1 - x_m)
if abs(x_n - x_m) < delta:
print("Settled on value for x_n: ", x_n)
break
else:
x_m = x_n # move forward to the next value
else:
print("x_n did not converge in 20000 terms")

How to apply recursion to an algorithm?

I am trying to write a predator-prey model where I take the input for the amount of rabbits, foxes, and years. Then output the final number of rabbits and foxes after that amount of years. I am able to return an amount of rabbits and foxes, but I am not getting the correct values. The algorithm for the foxes and rabbits after one year are:
F1yr = F0yr – Floor(F0yr * (G-S * R0yr))
R1yr = R0yr + Floor( R0yr * (A-B * F0yr))
Where A = 0.04, B = 0.0005, G = 0.2, and S=0.00005
For a starting input of 5891 rabbits and 16 foxes after 99 years, it should return 6484 rabbits and 144 foxes, but I am getting 4682 rabbits and 189 foxes.
This is the code that I have so far, I feel like I am close to the answer, but not fully there:
def bunnies(rabbits,foxes,years):
if __name__ == '__main__':
if years == 0:
tot = []
tot.append(rabbits)
tot.append(foxes)
return tot
else:
a = 0.04
b = 0.0005
g = 0.2
s = 0.00005
rabbits = rabbits + math.floor(rabbits * (a-b * foxes))
foxes = foxes - math.floor(foxes * (g-s * rabbits))
return bunnies(rabbits,foxes,years-1)
rabbits = int(input('Enter Initial Rabbit Population:\n'))
foxes = int(input('Enter Initial Fox Population:\n'))
years = int(input('Enter Number of Years to Simulate:\n'))
print(bunnies(rabbits,foxes,years))

Your code was almost correct, here is a fixed and cleaned up version:
import math
def bunnies(rabbits, foxes, years):
A = 0.04
B = 0.0005
G = 0.2
S = 0.00005
if years == 0:
return rabbits, foxes
else:
rabbits_last, foxes_last = rabbits, foxes
foxes = foxes_last - math.floor(foxes_last * (G - S * rabbits_last))
rabbits = rabbits_last + math.floor(rabbits_last * (A - B * foxes_last))
return bunnies(rabbits, foxes, years - 1)
if __name__ == '__main__':
rabbits = int(input('Enter Initial Rabbit Population: '))
foxes = int(input('Enter Initial Fox Population: '))
years = int(input('Enter Number of Years to Simulate: '))
print(bunnies(rabbits, foxes, years))
The problem ocurred when you used the already changed value of the rabbit population for the new fox population count.
You also used wrong variable names when calling print(bunnies(rab,fox,yrs)), but I think that was just a copying mistake since you didn't get error messages.
Lastly your if __name__ == '__main__' shouldn't have been inside the function but on the module scope like I have it.

Loop Table using distance = speed * time

The distance a vehicle travels can be calculated as follows:
distance = speed * time
Write a program that asks the user for the speed of a vehicle (in miles per hour) and how many hours it has traveled. The program should then use a loop to display the distance the vehicle has traveled for each hour of that time period. Here is an example of the output:
What is the speed of the vehicle in mph? 40
How many hours has it traveled? 3
Hour Distance Traveled
1 : 40
2 : 80
3 : 120
I've gotten everything done so far but can't manage to get the table to come out properly, as shown in the example table at the first hour (1) it should start at 40 but instead it starts at 120. Can someone help me fix the code? forgot to mention it should work for any value the user enters such as if someone was going 50 mph in 5 hours
g = 'y'
while g == 'Y' or g == 'y':
speed = int(input('Enter mph: '))
time = int(input('Enter hours: '))
if time <= 0 or speed <= 0:
print('Invalid Hours and mph must be greater than 0')
else:
for t in range(time):
distance = speed * time
print(t + 1,':', distance)
time = time * 2
g = 'n'
print('End')

Just change 2 things in your program. First, there's no need to double the time inside for loop, Second use variable t instead of time to calculate distance.
g = 'y'
while g == 'Y' or g == 'y':
speed = int(input('Enter mph: '))
time = int(input('Enter hours: '))
if time <= 0 or speed <= 0:
print('Invalid Hours and mph must be greater than 0')
else:
for t in range(time):
distance = speed * (t+1) // Use t+1 instead of time
print(t + 1,':', distance)
# time = time * 2 // No need to double the time
g = 'n'
print('End')
Input:
40
3
Output:
(1, ':', 40)
(2, ':', 80)
(3, ':', 120)
End

You need to remove the commas from the print line, and print out the numbers in string format and concat it to the string colon like:
print(str(t + 1) + ':' + str(distance))
You also need to increment the time by one not multiply by 2
time = time + 1
Your output distance also can be fixed by calculating it based on t instead of time
distance = speed * (t+1)

python 3.x overwrite previous terminal line

I wrote a simple program to calculate average outcome of a dice throw (pretty pointless, but you have to start somewhere ;P):
import random, time
from random import randrange
count = 0
total = 0
one_count = 0
for x in range(10000000):
random = randrange(1,7)
count = count + 1
total = total + random
average = total / count
percentage = one_count / count * 100
if random == 1:
one_count = one_count + 1
print("the percentage of ones occurring is", percentage, "and the average outcome is", average)
# time.sleep(1)
To clean it up I want the output to overwrite the previous line. I tried everything I could find, but the only thing I managed to to is to print to the same line without erasing the previous content by changing the last line to:
print("the percentage of ones occuring is", percentage, "and the average outcome is", average, "/// ", end="")
which outputs:
the percentage of ones occuring is 0.0 and the average outcome is 4.0 /// the percentage of ones occuring is 0.0 and the average outcome is 4.5 /// the percentage of ones occuring is 0.0 and the average outcome is 3.6666666666666665 ///
Any ideas?

Add a \r at the end. That way, the next line you write will start at the beginning of the previous line. And then flush output so it shows immediately.
Note: If the next line is shorter, the remaining characters will still be there.

use end='\r:
for x in range(100000):
rnd = randrange(1,7) # don't use random
count += 1
total = total + rnd
average = total / count
percentage = one_count / count * 100
if rnd == 1:
one_count += 1
print("the percentage of ones occurring is {} and the average outcome is {}".format(percentage,average),end='\r')
time.sleep(.1)
On another note using total = total + random is not a good idea, you are importing the random module and using random as a variable name.