Automatically saving plot, python, matplotlib

Question

I'd like to save my plot after it's finished. I've tried something like this:

import matplotlib.pyplot as plt
import os

plt.ion()
x = []
y = []
home = os.sep.join((os.path.expanduser('~'), 'Desktop'))
home1 = home + '\nowy'

for i in range(0,20):
    x.append(i)
    y.append(i+2)

    plt.plot(x, y, 'g-', linewidth=1.5, markersize=4)
    plt.axis(xmin = 0,xmax = 200,ymin=0,ymax=200)
    plt.show()
    plt.pause(0.1)
plt.pause(5)
plt.savefig(os.sep.join(home1 + '1'),format = 'png')

But it does not work. Thers is an error:

[Errno 22] invalid mode ('wb') or filename: 'C\\:\\\\\\U\\s\\e\\r\\s\\\\\\M\\i\\c\\h\\a\\l\\\\\\D\\e\\s\\k\\t\\o\\p\\\n\\o\\w\\y\\p\\l\\o\\t\\1.png'

Can anyone tell me how to save this plot exactly in direction "home1", please? I've serched for sollution for a while but nothing worked.

j-i-l · Accepted Answer · 2014-08-10 21:59:15Z

4

Try it with os.path.join:

plt.savefig(os.path.join(os.path.expanduser('~'), 'Desktop', 'nowy1.png'))

Alternatively you can use os.sep.join, which makes your code more compatible. It could look somehow like this:

plt.savefig(os.sep.join([os.path.expanduser('~'), 'Desktop', 'nowy1.png']))

edited Aug 10, 2014 at 21:59

answered Aug 10, 2014 at 17:54

j-i-l

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6 Comments

Maq92 Over a year ago

Thak You very much :)

j-i-l Over a year ago

@Maq92: Well your code has several plt.pause calls in it, try to remove the last one before saving the current figure.

Maq92 Over a year ago

No, the last pause have to be there. I'm talking about this time before "updateing" grapht (getting new point and draw it). I'm going to draw some huge graphs with it and don't want to wait few hours for it :) Is there any way to boost it?

j-i-l Over a year ago

@Maq92 Do you need to draw the current figure in every step when you add new data? Based on the size of the data you want to show, plt.draw just takes some time and at least to my knowledge there is not much you can do to speed it up. But for the example code you have here, the time you need to wait should virtually be determined by the plt.pause calls.

Maq92 Over a year ago

This will be a program that draws (and live update) a graph based on data recived from external equipement. Hm, ok thanks for help :)

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tacaswell · Accepted Answer · 2014-08-10 22:01:34Z

If you are going to be running this automatically it is better to use the OO interface rather than the state machine interface:

import matplotlib.pyplot as plt
import os

plt.ion()
x = []
y = []
home = os.path.join(os.path.expanduser('~'), 'Desktop')
home1 = os.path.join(home, 'nowy')

# create the figure and axes
fig, ax = plt.subplots(1, 1)
ax.set_xlim(0, 200)
ax.set_ylim(0, 200)

# create the line2D artist
ln, = ax.plot(x, y, 'g-', linewidth=1.5, markersize=4)
# do the looping
for i in range(0,20):
    # add to the data lists
    x.append(i)
    y.append(i+2)
    # update the data in the line2D object
    ln.set_xdata(x)
    ln.set_ydata(y)
    # force the figure to re-draw
    fig.canvas.draw()
    # pause, let the gui re-draw it's self
    plt.pause(0.1)
# pause again?
plt.pause(5)
# save the figure
fig.savefig(os.path.join(home1,  '1'),format='png')

[not tested, due to discovering an unrelated bug in RC3]

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