How to iterate until a condition is met in python for loop

Question

I have been working on this simple interest calculator and I was trying to make the for loop iterate until the amount inputted by the user is reached. But I am stuck at the range part, if I assign a range value like range(1 ,11) it will iterate it correctly and print the year in in contrast to the amount but I want the program to iterate until the year in which principal is greater than the amount is reached. My current code is bellow and the final product I want to reach is also attached bellow the current code. I’m new to python so please bare with me if I’m of track. Thanks in advance.

Current code:

principal = float(input("How much money to start? :"))
apr = float(input("What is the apr? :"))
amount = float(input("What is the amount you want to get to? :"))

def interestCalculator():
    global principal
    year = 1
    for i in range(1, year + 1):
        if principal < amount:
            principal = principal + principal*apr
            print("After year " + str (i)+" the account is at " + str(principal))
            if principal > amount:
                print("It would take" + str(year) + " years to reach your goal!")
        else:
            print("Can't calculate interest. Error: Amount is less than principal")

interestCalculator();

Final expected result:

Asked By: sarem dave

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Source

Answer 1

Instead, you can use a while loop. What I mean here is you can simply:

principal = float(input("How much money to start? :"))
apr = float(input("What is the apr? :"))
amount = float(input("What is the amount you want to get to? :"))


def interestCalculator():
    global principal
    i = 1

    if principal > amount:
        print("Can't calculate interest. Error: Amount is less than principal")

    while principal < amount:
        principal = principal + principal*apr
        print("After year " + str (i)+" the account is at " + str(principal))
        if principal > amount:
            print("It would take" + str(year) + " years to reach your goal!")
        i += 1


interestCalculator()

Answered By: Daniyar Aubekerov

Answer 2

A suggestion for a more pythonic solution

PRINCIPAL = float(input("How much money to start? :"))
APR = float(input("What is the apr? :"))
AMOUNT = float(input("What is the amount you want to get to? :"))


def interestCalculator(principal, apr, amount):
    year = 0
    yield year, principal
    while principal < amount:
        year += 1
        principal += principal*apr
        yield year, principal


for year, amount in interestCalculator(PRINCIPAL, APR, AMOUNT):
    print(f"After year {year} the account is at {amount:.2f}")

if year == 0:
    print("Can't calculate interest. Error: Amount is less than principal")
print(f"It would take {year} years to reach your goal!")

Answered By: Holger Bille

How to iterate until a condition is met in python for loop

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