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, Dec 12 '17 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, Dec 12 '17 at 19:43

scharette · Answer 1 · 2017-12-13T14:36:44.800

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 '17 at 14:36

answered Dec 12 '17 at 19:49

scharette

9,437
8
33
67

@FredLarson can you please elaborate? I can't understand what you're underlying. – scharette Dec 12 '17 at 19:59
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 Dec 12 '17 at 20:14
Brain fade -- I had said `elif:` when I meant `else:`. Sorry. – Fred Larson Dec 12 '17 at 20:19
@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... – scharette Dec 13 '17 at 14:35
You're right, `else: pass` doesn't make a whole lot of sense. Good work. – Fred Larson Dec 13 '17 at 16:36

score 0 · Answer 2 · edited Dec 12 '17 at 20:05

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.

Aaditya Ura · Answer 3 · 2017-12-12T20:06:48.270

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

Converting an empty string input to float

3 Answers3

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