ValueError with input and trying to convert input value into int

Question

I am a beginner, so please bear with me. I am trying to solve a very simple question but am getting a consistent error with the input and int commands. The problem I am trying to solve is the following:

You have a debt of 50k€. You compare different deposits and the most profitable one is a deposit with a 6% annual compound interest. How much money should you invest in that deposit to have 50k€ in N years?

My code is:

FV=50000   #future value of the deposit is 50,000 euros
I=0.06     #the interest rate of the deposit is 6%
N=input("number of months:")
N=int(N)
print(FV/(1+I)**N)
print("I should invest", FV/(1+I)**N, "euros to have", FV, " euros in", N, 
"months with interest", I)

But the kernel stops running and executing after the third line (input command) and when I manually hit Enter to get a newline, I get a ValueError code that says:

ValueError: invalid literal for int() with base 10: ''

Can someone tell me why I am getting this error? And where am I wrong in solving the problem? Thanks in advance.

What happens when you input a number and hit enter? Just hitting enter will input ''. — timgeb
– timgeb, Commented Nov 11, 2018 at 17:30
When there is a prompt, you should enter number. If you press enter without number, empty string is read which is invalid literal for int(). — Austin
– Austin, Commented Nov 11, 2018 at 17:34
I don´t understand your question, timgeb. I hit Enter in the kernel in order to get a newline, because the kernel stops executing after the third line of code, but I don´t know what number to enter since I don´t know the value of N (number of months), which is part of what I´m trying to solve for... — Madrid_datalady
– Madrid_datalady, Commented Nov 11, 2018 at 17:41
The kernal doesnt "stop", it is waiting for you to input N. you aren't solving for a value of N, N is being provided here. you are trying to solve for the initial investment with some value of N that needs to be provided. When you press enter however, you just feed it an empty string, which causes int(N) to fail because it is int('') — Paritosh Singh
– Paritosh Singh, Commented Nov 11, 2018 at 17:43

Paritosh Singh · Accepted Answer · 2018-11-11 17:56:47Z

2

The code seems to work fine. i am going to add a couple of print statements that may help make things clearer. See if this helps.

FV=50000   #future value of the deposit is 50,000 euros
I=0.06     #the interest rate of the deposit is 6%
print("I am a computer program, i am about to ask you for an input. please enter something and then press enter")
N=input("number of years:")
if N != '': #can be replaced with if N:
    print("you have entered-",N)
else:
    print("that is an empty string")
N=int(N)
print(FV/(1+I)**N)
print("I should invest", FV/(1+I)**N, "euros to have", FV, " euros in", N, 
"years with interest", I)

edited Nov 11, 2018 at 17:56

answered Nov 11, 2018 at 17:48

Paritosh Singh

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3 Comments

Madrid_datalady Over a year ago

Thank you very much, Paritosh! I understand now and it worked... Also, N should be "number of years", not "number of months", since the interest rate is annual, so I changed that. Thank you, your explanations was really helpful!

Paritosh Singh Over a year ago

Glad to help. Welcome to programming, don't be afraid to experiment with things and use lots of print statements whenever stuck! :) @Madrid_datalady

timgeb Over a year ago

@Madrid_datalady if the question is solved, please accept the answer by clicking the green checkmark to say thank you to Paritosh.

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