Value error when converting string to float-CodePudding

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()

CodePudding user response：

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']

CodePudding user response：

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.

CodePudding user response：

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.