ValueError: could not convert string to float in simple code

Question

       # -*- coding: cp1250 -*-
print ('euklides alpha 1.0')
a = raw_input('podaj liczbę A  : ')
b = raw_input('podaj liczbę B  : ')

a = float('a')
b = float('b')

if 'a'=='b':
    print 'a'
elif 'a' > 'b':
    while 'a' > 'b':
        print('a'-'b')
        if 'a'=='b': break
        if 'a' > 'b': continue
elif 'b' > 'a':
    while 'b' > 'a':
        print('b'-'a')
        if 'b'=='a': break
        if 'b' > 'a': continue

So, this is a code, which I made few hours ago. Now I get a ValueError: could not convert string to float: a, and I have no idea why. Can you explain it to me? I'm a beginner.

Why are you making everything strings? 'a' is the character a - a (no quotes) is the variable name a... So float('a') is wrong - you can't make a float from the letter a - it should be float(a) where a will be the content of what's been entered... — Jon Clements
– Jon Clements, Commented Dec 2, 2013 at 21:48

jramirez · Accepted Answer · 2013-12-02 21:57:38Z

the float function can take a string but it must contain a possibly signed decimal or floating point number. You want to make the variable a a float not the char 'a'.

You don't need all the ' around your variable names. When you put quotes around them 'b' you are making them a string.

On another note once you reach on of those while statements there's nothing that will get you out of there.

a = float(a)


if a == b: # you need to get rid of all the ' unless you are talking about chars 



   # -*- coding: cp1250 -*-
print ('euklides alpha 1.0')
a = raw_input('podaj liczbę A  : ')
b = raw_input('podaj liczbę B  : ')

a = float('a')
b = float('b')

if a==b:
    print a
elif a > b:
    while a > b: # nothing will get you out of the while loop
        print(a-b)
        if a == b:
            break
        if a > b: # no need for this if, the while loop will do that check for you
            continue
elif b > a:
    while b > a: # nothing will get you out of the while loop
        print(b-a)
        if b==a:
            break
        if b > a: # no need for this if, the while loop will do that check for you
            continue

Community · Accepted Answer · 2017-05-23 12:19:14Z

1

You're enclosing all your variables in single quotes, so you're comparing the string "a" with the string "b" rather than the floating point number contained in variable a with the same in variable b

Also worth pointing out:

This is your original code, to request two floating point numbers from the user

a = raw_input('podaj liczbę A  : ')
b = raw_input('podaj liczbę B  : ')
a = float(a)
b = float(b)

If you're in Python 2.x, you can instead use

I was corrected by abarnert in comments below. Just leaving it for edification:

I wouldn't suggest using input instead of raw_input and float. The latter guarantees that you get floats; the former could get, say, the result of calling __import__('os').system('rm -rf /'), which is probably something you don't want

a = input('podaj liczbę A  : ')
b = input('podaj liczbę A  : ')

If you're not, you may want to include a try/catch block that will force the variable to be of the type you require

a_verifying = True
while a_verifying:
  a = input('podaj liczbę A  : ')
  try:
    a = float(a)
    a_verifying = False
  except ValueError as e:
    a = input('podaj liczbę A  : ')

b_verifying = True
while b_verifying:
  b = input('podaj liczbę B  : ')
  try:
    b = float(b)
    b_verifying = False
  except ValueError as e:
    b = input('podaj liczbę B  : ')

edited May 23, 2017 at 12:19

CommunityBot

11 silver badge

answered Dec 2, 2013 at 21:51

Adam Smith

54.6k13 gold badges84 silver badges120 bronze badges

2 Comments

abarnert Over a year ago

I wouldn't suggest using input instead of raw_input and float. The latter guarantees that you get floats; the former could get, say, the result of calling __import__('os').system('rm -rf /'), which is probably something you don't want.

Adam Smith Over a year ago

abarnert: I defer to your opinion. I only started using Python recently, and when I started I learned "input() for numbers, raw_input() for strings." Now I'm in 3.x and don't care about such distinctions :)

Collectives™ on Stack Overflow

ValueError: could not convert string to float in simple code

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related