Python: String will not convert to float

Question

I wrote this program up a few hours ago:

while True:
    print 'What would you like me to double?'
    line = raw_input('> ')
    if line == 'done':
        break
    else:
        float(line)              #doesn't seem to work. Why?
        result = line*2
        print type(line)         #prints as string?
        print type(result)       #prints as string?
        print " Entered value times two is ", result

print 'Done! Enter to close'

As far as I can tell, it should be working fine.The issue is that when I input a value, for example 6, I receive 66 instead of 12. It seems like this portion of code:

float(line)

is not working and is treating line as a string instead of a floating point number. I've only been doing python for a day, so its probably a rookie mistake. Thanks for your help!

score 7 · Answer 1 · answered May 14 '13 at 03:13

7

float() returns a float, not converts it. Try:

line = float(line)

answered May 14 '13 at 03:13

Marcelo

9,916
3
43
52

Thanks! I knew it was just a rookie mistake. Thanks for the quick response, as I was refusing to go to sleep until I solved the issue. – Philosopher May 14 '13 at 03:17
1

In fact, it is not possible to convert the value "in-place" - the language doesn't work that way. In Python, variables don't have types, but values do, and those types don't change. You just create new values representing the "converted" result. – Karl Knechtel May 14 '13 at 03:21

Srikar Appalaraju · Accepted Answer · 2013-05-14T03:34:01.923

float(line) does not convert in-place. It returns the float value. You need to assign it back to a float variable.

float_line = float(line)

UPDATE: Actually a better way is to first check if the input is a digit or not. In case it is not a digit float(line) would crash. So this is better -

float_line = None
if line.isdigit():
    float_line = float(line)
else:
    print 'ERROR: Input needs to be a DIGIT or FLOAT.'

Note that you can also do this by catching ValueError exception by first forcefully converting line and in except handle it.

try:
    float_line = float(line)
except ValueError:
    float_line = None

Any of the above 2 methods would lead to a more robust program.

This is the best solution. The name `line` is not appropriate for the resulting value. Even better would be `value = float(line)` and then continue with that. — glglgl, May 14 '13 at 03:18

score 2 · Answer 3 · answered May 14 '13 at 03:13

2

float(line) doesn't change line at all, so it is still a string. You'll want to use line = float(line) instead.

answered May 14 '13 at 03:13

Simon

10,679
1
30
44

Python: String will not convert to float

3 Answers3

Linked

Related