matplotlib + wxpython not sizing correctly with legend

Question

I have a matplotlib figure embedded in a wxpython frame with a few sizers. Everything works fine until I include a legend but then the sizers don't seem to be working with the legend.

Even when I resize the window by dragging at the corner, the main figure changes size, but only the edge of the legend is ever shown.

That is, note that the legend is not visible in the wxFrame.

import wx
import matplotlib as mpl
from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg as Canvas
from random import shuffle  

class PlotFrame(wx.Frame):

    def __init__(self):     

        wx.Frame.__init__(self, None, -1, title="Plot", size=(-1, -1))
        self.main_panel = wx.Panel(self, -1)
        self.plot_panel = PlotPanel(self.main_panel)

        s0 = wx.BoxSizer(wx.VERTICAL)
        s0.Add(self.main_panel, 1, wx.EXPAND)
        self.SetSizer(s0)
        self.s0 = s0

        self.main_sizer = wx.BoxSizer(wx.VERTICAL)        
        self.main_sizer.Add(self.plot_panel, 1, wx.EXPAND)        
        self.main_panel.SetSizer(self.main_sizer)       

class PlotPanel(wx.Panel):

    def __init__(self, parent, id = -1, dpi = None, **kwargs):
        wx.Panel.__init__(self, parent, id=id, **kwargs)
        self.figure = mpl.figure.Figure(dpi=dpi, figsize=(2,2))
        self.canvas = Canvas(self, -1, self.figure)

        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(self.canvas,1,wx.EXPAND)
        self.SetSizer(sizer)
        sizer.SetMinSize((600, 500))
        self.sizer = sizer

def test(plot_panel):
    axes = plot_panel.figure.gca()
    for c in ['r', 'b', 'k']:
        vals = [20, 30, 40, 50, 80, 20, 50, 60, 70, 70, 80]
        shuffle(vals)
        axes.plot(range(len(vals)), vals, "-o", color=c, label=c*10)
    legend = axes.legend(loc='center left', bbox_to_anchor=(1.05, 0.5))
    return legend

if __name__=="__main__":
    app = wx.PySimpleApp()
    frame = PlotFrame()
    legend = test(frame.plot_panel)
    frame.Fit()
    print "legend frame pre show: ", legend.get_frame()
    frame.Show(True)
    print "legend frame post show:", legend.get_frame()
    frame.Fit()
    app.MainLoop()

Edit:
For a solution to be useful to me, I would like it to look good when the figure is automatically drawn by the program, so adjustment parameters can be hard coded in the program, or, for example, on a window resize event, but not adjusted by hand for each plot. The main things that I expect to change here are: 1) the lengths of the labels (from, say, 1 to 25 characters), 2) the windows size (usually by the user dragging around the corner, and 3) the number of points and lines. (Also, if it matters, eventually, I'll want to have dates on the bottom axis.)

I've put the legend outside of the axes so that it won't cover any data points, and I'd prefer that it stay to the right of the axes.

I'm using Python 2.6.6, wxPython 2.8.12.1, and matplotlib 1.1.0 and am stuck with these for now.

Answer 1

It is re-sizing correctly, you just didn't tell it to do what you want it to do.

The problem is this line:

axes.legend(loc='center left', bbox_to_anchor=(1.05, 0.5))

Pretty sure the bbox_to_anchor kwarg is over-ridding the loc kwarg and you are pegging the bottom left of the legend to (1.05, 0.5) in axes units. If the axes expands to fill your window, the left edge of the legend will always be 5% of the width axes to the right of the right edge of you axes, hence always out of view.

You either need to put your legend someplace else or shrink your axes (in figure fraction).

option 1 move the legend:

axes.legend(bbox_to_anchor=(0.5, 0.5)) #find a better place this is in the center

option 2 move the axes + resize the figure:

axes.set_position([.1, .1, .5, .8]) # units are in figure fraction

set_position

fig = figure()
axes = fig.add_subplot(111)

for c in ['r', 'b', 'k']:
    vals = [20, 30, 40, 50, 80, 20, 50, 60, 70, 70, 80]
    shuffle(vals)
    axes.plot(range(len(vals)), vals, "-o", color=c, label=c*10)

legend = axes.legend(loc='center left', bbox_to_anchor=(1.05, 0.5))

# adjust the figure size (in inches)
fig.set_size_inches(fig.get_size_inches() * np.array([1.5, 1]), forward=True)

# and the axes size (in figure fraction)
# to (more-or-less) preserve the aspect ratio of the original axes
# and show the legend
pos = np.array(axes.get_position().bounds)
pos[2] = .66
axes.set_position(pos)

option 3: automate option 2

fig = figure() # use plt to set this up for demo purposes
axes = fig.add_subplot(111) # add a subplot

# control paramters 
left_pad = .05 
right_pad = .05

# plot data
for c in ['r', 'b', 'k']:
    vals = [20, 30, 40, 50, 80, 20, 50, 60, 70, 70, 80]
    shuffle(vals)
    axes.plot(range(len(vals)), vals, "-o", color=c, label=c*10)
# set axes labels
axes.set_xlabel('test x')
axes.set_ylabel('test y')

# make the legend
legend = axes.legend(loc='center left', bbox_to_anchor=(1 + left_pad, 0.5))

# function to 'squeeze' the legend into place
def squeeze_legend(event):
    fig.tight_layout()
    right_frac = 1 - legend.get_window_extent().width / fig.get_window_extent().width - left_pad - right_pad
    fig.subplots_adjust(right=right_frac)
    fig.canvas.draw()

# call it so the first draw is right
squeeze_legend()

# use the resize event call-back to make sure it works even if the window is re-sized
fig.canvas.mpl_connect('resize_event', squeeze_legend)