Converting String to Float in matplotlib generates Error

Question

I am trying to convert some numbers represented as strings but I get an error!

Here is my code

import numpy as np
import matplotlib.pyplot as plt

a = np.linspace(-np.pi*2, np.pi*2, 200)
b = np.cos(a)

fig, ax = plt.subplots()

ax.plot(a, b)

fig.canvas.draw()

labels = [item.get_text() for item in ax.get_xticklabels()]

labels = [float(label) for label in labels]

float(labels[-1]) # this works

error : labels = [float(label) for label in labels] ValueError: could not convert string to float: '−8'

labels, in this case, can be generated as [str(i) for i in range(-8, 9, 2)] which I can convert its items to float but not the text of the label retrieved from matplotlib!

I believe the issue is with the - sign.

since when i check '-8' in labels gives False

but '8' in labels gives True

Gabriel Avendaño · Accepted Answer · 2019-10-09 20:58:36Z

3

One solution is to replace the unicode character U+002D to U+2212. this answer can help you with that. But it also says that it's not very recomended. You can use instead ax.get_xticks()

print(ax.get_xticks())
output : [-8. -6. -4. -2.  0.  2.  4.  6.  8.]

answered Oct 9, 2019 at 20:58

Gabriel Avendaño

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Comments

jjramsey · Accepted Answer · 2019-10-09 20:22:16Z

1

I believe the issue is with the - sign.

It is, sort of. The problem is that in the string that could not be converted, the character in front of the '8' is not an ASCII hyphen (with Unicode codepoint U+002D) but rather the Unicode character for a minus sign (with Unicode codepoint U+2212). Those characters look very similar, but Python only treats the first one as a minus sign.

answered Oct 9, 2019 at 20:22

jjramsey

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2 Comments

Khalil Al Hooti Over a year ago

do you have any idea how can I convert it to an understandable minus sign for python

jjramsey Over a year ago

@KhalilAlHooti The replace method for strings should do it, something like label.replace("\u2212", "-"). But I think Gabriel's answer is better.

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