Value error when converting string to float

Question

it is showing value error for converting string into float. one of the line of my data file looks like this 100 1.2811559340137890E-003 I think maybe python can't understand E while converting. also following is my code

import math
import matplotlib.pyplot as plt
x = []
y = []
f= open('C:/Users/Dell/assignment2/error_n.dat', 'r')
for line in f:
    line= line.split(' ')

    x.append(line[0])
    y.append(line[1])
for i in range(0,4):
    x[i]=float(x[i])
    x[i]=math.log(x[i])
    y[i]=float(y[i])
    y[i]=math.log(y[i])
        

plt.plot(y, x, marker = 'o', c = 'g')

plt.show()

Always show us the full traceback message - it will indicate the exact string value that failed to be converted to a float. — jasonharper
– jasonharper, Commented Feb 14, 2022 at 17:15

at54321 · Accepted Answer · 2022-02-14 17:13:23Z

1

The string 1.2811559340137890E-003 can be converted to float without a problem. You can easily try this in the Python shell:

>>> s = '1.2811559340137890E-003'
>>> float(s)
0.001281155934013789

However, you're actually trying to convert an empty string. See why:

>>> line = '100   1.2811559340137890E-003'
>>> line.split(' ')
['100', '', '', '1.2811559340137890E-003']

To solve your problem, simply change line.split(' ') to line.split():

>>> line.split()
['100', '1.2811559340137890E-003']

answered Feb 14, 2022 at 17:13

at54321

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Comments

Orius · Accepted Answer · 2022-02-14 17:15:24Z

0

I think the problem is that when you split that line, the second item (y) is "" (an empty string), and that's the one which can't be converted into a number.

answered Feb 14, 2022 at 17:15

Orius

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Comments

sirakiin · Accepted Answer · 2022-02-14 17:18:23Z

0

float is able to handle scientific notations. However from your description, it seems like the ValueError was thrown from trying to convert empty string to float.

'100   1.2811559340137890E-003'.split(' ')

will return

['100', '', '', '1.2811559340137890E-003']

You can check the string before converting it to float to handle such error.

answered Feb 14, 2022 at 17:18

sirakiin

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