Re: [Matplotlib-users] how to make matplotlib faster?

[Matt N. <new...@ca...>]

Hi,

I'm doing relatively simple line plots the WXAgg backend, but I
also find matplotlib to be somewhat slower than I'd hope for.

On a WindowsXP box (P4 1.7GHz, 512Mb RAM), in a wx event loop
issuing a plot() as fast as I can go, I get about 1 plot every
0.25 to 0.30 sec.  This is just barely fast enough for my needs.  
If I could reliably go at 10 plots/sec, that would be great.

It turns out that the dynamic_demo_wx.py example does go much
faster, but it does not actually re-do a plot(). Instead it just
changes the subplots line data.  That's interesting, but I need
the view to be adjusted as well, as the scale will change with
time for my data.  So far, I'm just re-issuing plot(), but I'd be
willing to do something slightly fancier.

Anyway, that led me to try to track down where the slowness in
plot() was coming from. Using nothing more sophisticated than
print statements, I believe the performance bottleneck is in
axis.py in Axis.draw(), in this block:

        for tick, loc, label in zip(majorTicks, majorLocs, majorLabels):
            if not interval.contains(loc): continue
            seen[loc] = 1
            tick.update_position(loc)
            tick.set_label1(label)
            tick.set_label2(label)            
            tick.draw(renderer)
            extent = tick.label1.get_window_extent(renderer) 
            ticklabelBoxes.append(extent)

For me, this block (run twice for a plot()) typically takes at
least 50% of the plot time.  Commenting out the
tick.draw(renderer) and the following two 'extent' lines roughly
doubles the drawing rate (though no grid or ticks are shown). I
was surprised by this, but have not tracked it down much beyond
this.  I'm not using mathtext in the labels and had only standard
numerical Tick labels in this example.

I don't know if this is applicable to the slowness of the contour
plots or error bars or if collections would help here.  But it
doesn't seem like tick drawing should be the bottleneck. Anyway,
this seems like a simple place to test in other situations, and
may be a good place to look for possible optimizations.

Thanks, 

--Matt