Plotting functions from a list using matplotlib

Question

I have been trying to print several equations I have using numpy and matplotlib.

The functions are stored on a text file, one equation per line. These equations look like this: np.exp(6.6506+(-171.637)/(x*32))

My idea was to iterate to each line, generate the plot and save it somewhere. My code:

import numpy as np
import matplotlib.pyplot as plt

source = "path/to/list.txt"

with open(source) as f:
    for line in f.readlines():
        x = np.linspace(0,200)
        y = line
        plt.plot(x,y)
        plt.savefig(str( line + ".png"))
        plt.close()

I get the results I want by removing the loops part and replacing y = line by y = np.exp(6.6506+(-171.637)/(x*32))

How can I plot all equations in my txt file? Plots are very simple and 2D.

Reblochon Masque · Accepted Answer · 2016-04-24 11:49:57Z

2

Use eval, with the usual reservations regarding security:

y = eval(line)

you may have to remove the new line \n from the lines you read from file with line.strip('\n')

drawing attention to eval security risks:

eval parses a string (any string given to it) and attempts to execute it... This is why it is generally considered a security risk and must only be used when it is certain that no malicious or harmful instructions will ever be passed to it. The risks involved are not trivial and the consequences potentially disastrous.

more about the dangers of eval - suggested by @Brenogil

edited Apr 24, 2016 at 11:49

answered Apr 23, 2016 at 17:42

Reblochon Masque

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3 Comments

brenogil Over a year ago

Thanks! What does eval() do in this case?

Reblochon Masque Over a year ago

eval parses a string (any string given to it) and attempts to execute it... This is why it is generally considered a security risk and must only be used when it is certain that no malicious or harmful instructions will ever be passed to it. The risks involved are not trivial and the consequences potentially disastrous.

brenogil Over a year ago

Thanks! This solved it. Your clarifications were quite nice. I also checked this post: eval really is dangerous

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