CODEWITHSUNDEEP
pythonmatplotlib
M. Steinke
M. Steinke

Reputation: 41

Event handling: Matplotlib's Figure() and pyplot's figure()

As desribed in http://matplotlib.org/users/event_handling.html the following example code works fine

import matplotlib.pyplot as plt

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)

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

But why does

from matplotlib.figure import Figure

fig = 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)

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

not work (although it is basically the same)? The error is

AttributeError: 'NoneType' object has no attribute 'mpl_connect'

This really confuses me, as

type(fig)

gives as expected the same result in both cases:

<class 'matplotlib.figure.Figure'>

Upvotes: 4

Views: 2236

Answers (1)

Anand S Kumar
Anand S Kumar

Reputation: 91009

That is because when you create a standalone Figure instance using Figure() , the canvas is not automatically set , you have to set the canvas using the method - fig.set_canvas() . Since you did not do this fig.canvas is None and when you tried to - fig.canvas.mpl_connect you got the AttributeError .

But when you use pyplot and get the figure using - plt.figure() - it creates the canvas for you. If you are wondering where , then matplotlib.pyplot.figure() internally uses matplotlib.backend.new_figure_manager() to create the figure, and that (depending on the backend) creates the figure , Example for gtk it is available here - line 99 -

canvas = FigureCanvasGTK(figure)

Upvotes: 6

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