Why can't I plot chosen points?

Question

In Matplotlib, Python, I want to click and mark points (actually, a point calculated from its position, eventually), but it doesn't seem to be possible. Even something simple like this doesn't work:

from pylab import *

fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(np.random.rand(10))

def onclick(event):
    print 'button=%d, x=%d, y=%d, xdata=%f, ydata=%f'%(
        event.button, event.x, event.y, event.xdata, event.ydata)
    plt.plot(event.xdata,event.ydata,',')

cid = fig.canvas.mpl_connect('button_press_event', onclick)
show()

score 1 · Answer 1 · answered Nov 26 '13 at 06:06

1

',' is the marker for a single pixel, try 'o' or something larger instead.

fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(np.random.rand(10))

def onclick(event):
    print 'button=%d, x=%d, y=%d, xdata=%f, ydata=%f'%(
        event.button, event.x, event.y, event.xdata, event.ydata)
    ax.plot(event.xdata,event.ydata,'o')
    plt.draw_if_interactive()

cid = fig.canvas.mpl_connect('button_press_event', onclick)
show()

enter image description here

answered Nov 26 '13 at 06:06

tacaswell

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I used ',' as marker before. with o, no change, still doesn't work. – NoBugs Nov 26 '13 at 06:08
The code I posted works correctly on current master. What version of mpl are you using? – tacaswell Nov 26 '13 at 06:10
@NoBugs Also, what backend? Interactivity does not work in ipython notebooks – tacaswell Nov 26 '13 at 06:17
Version 1.2.1, using whatever Ubuntu default is. – NoBugs Nov 26 '13 at 06:19
@NoBugs Are you running this through an interactive shell or through a script? – tacaswell Nov 26 '13 at 06:32
I just saved the file and ran it. (Using Geany) – NoBugs Nov 26 '13 at 07:03
the interactive features do not always play nice with scripts, try the same code in an interactive session and I bet it will work. – tacaswell Nov 26 '13 at 07:33
Why would that be different? I need to copy paste to python terminal? – NoBugs Nov 26 '13 at 15:32
See the discussion here: https://github.com/matplotlib/matplotlib/pull/2503 run your script with `python -i run.py` – tacaswell Nov 26 '13 at 17:33
1

Can you try running it in `ipython --pylab` (which makes sure all of the gui magic is started up properly) to verify that `matplotlib` is working correctly? – tacaswell Nov 27 '13 at 04:52
That works! It says "Welcome to pylab, a matplotlib-based Python environment [backend: TkAgg]." How do I set the backend from my python code though? – NoBugs Nov 27 '13 at 15:30
Why do you use draw_if_interactive() when draw() works perfectly, running the script as a file? – NoBugs Dec 01 '13 at 02:42
Because this is an interactive feature. – tacaswell Dec 01 '13 at 06:42

Why can't I plot chosen points?

1 Answers1