Converting an empty string input to float

Question

I made a code like this to find the arithmetical mean for numbers the user has typed in but for some reason the program couldn't convert string to float in the end. What should I change?

print("I'm going to find the arithmetical mean! \n")
jnr = 0; sum = 0
negative = "-"
while True:
    x = input(f"Type in {jnr}. nr. (To end press Enter): ")
    if negative not in x:
        jnr += 1
    elif negative in x:
        pass
    elif x == "": break
    sum = sum + float(x)

print("Aritmethmetical mean for these numbers is: "+str(round(sum/(jnr-1), 2)))

I got his Error :

Traceback (most recent call last): File "C:\Users\siims\Desktop\Koolitööd\individuaalne proge.py", line 11, in sum = sum + float(x) ValueError: could not convert string to float

What is the error that you get? Please provide any tracebacks or input or output in your question. — Max
– Max, Commented Dec 12, 2017 at 19:42
round() is not the error. The error comes from the fact that you're trying to call float(x) which is an invalid string to convert when the user press enter. — scharette
– scharette, Commented Dec 12, 2017 at 19:43

scharette · Accepted Answer · 2017-12-13 14:36:44Z

3

As I said in my comment the error comes from the fact that calling float(x) when the user uses Enter result in the error. The easiest way to fix your code without changing everything is by checking first if the input is "". That way you will not be trying to convert an empty string to float.

print("I'm going to find the arithmetical mean! \n")
jnr = 0; 
sum = 0
negative = "-"
while True:
    x = input(f"Type in {jnr}. nr. (To end press Enter): ")

    if x == "":
        break
    elif negative not in x:
        jnr += 1
        sum = sum + float(x)


print("Aritmethmetical mean for these numbers is: "+str(round(sum/(jnr-1), 2)))

edited Dec 13, 2017 at 14:36

answered Dec 12, 2017 at 19:49

scharette

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5 Comments

scharette Over a year ago

@FredLarson can you please elaborate? I can't understand what you're underlying.

Fred Larson Over a year ago

If negative not in x is false, negative in x must be true. The second test is redundant, so eliminate it. Just else: will do.

Fred Larson Over a year ago

Brain fade -- I had said elif: when I meant else:. Sorry.

scharette Over a year ago

@FredLarson Ok haha, now I see. I wanted to keep the code as original as possible. You are right, but using else would also be redundant in my opinion, since else: pass will be ignored by the compiler...

Fred Larson Over a year ago

You're right, else: pass doesn't make a whole lot of sense. Good work.

PinkClimbingApple · Accepted Answer · 2017-12-12 20:05:18Z

0

You're trying to convert a string to a float but it is an invalid string if you are using the string for that purpose. I would just continue asking until the user gives the right input, like this:

def float_input(s):
    while True:
        try:
            x = input(s)
        except ValueError:
            print('Invalid input. Try again.')
        else:
            break
    return x

Then, instead of input, use float_input in your code.

edited Dec 12, 2017 at 20:05

PinkClimbingApple

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answered Dec 12, 2017 at 19:59

user1781434

Comments

Aaditya Ura · Accepted Answer · 2017-12-12 20:06:48Z

0

An updated version of your code :

print("I'm going to find the arithmetical mean! \n")
jnr = 0; sum = 0
while True:
    x = int(input())
    if x>1:
        jnr += 1
    elif x<1:
        pass

    if x == 0:
        break
    sum += float(x)
    print(sum)



print("Aritmethmetical mean for these numbers is: {}".format(sum/jnr))

output:

I'm going to find the arithmetical mean! 

9
9
9
9
9
0
Aritmethmetical mean for these numbers is: 9.0

Pythonic way:

You can find mean by:

print("I'm going to find the arithmetical mean! \n")
inp=[int(i) for i in input().split()]
print(sum(inp)/len(inp))

output:

I'm going to find the arithmetical mean! 

9 9 9 9 9
9.0

edited Dec 12, 2017 at 20:06

answered Dec 12, 2017 at 20:01

Aaditya Ura

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