Re: [Matplotlib-users] Calling xlim makes x tick labels format get lost

[Goyo <goy...@gm...>]

El dom, 12-10-2008 a las 13:22 -1000, Eric Firing escribió: 
> Goyo wrote:
> > Hi all,
> > 
> > I'm plotting time series and using a custom format for x tick labels
> > because I want to see both date and time. But calling xlim makes the
> > default format return -- only dates or only times, it depends on the
> > displayed interval.
> > 
> > I can get my preferred format back by calling set_major_formatter again,
> > but this is inconvenient for interactive use.
> > 
> > I wonder if there is a better way for changing x limits while keeping
> > tick labels format unchanged.
> > 
> > I'm using matplotlib 0.98.3
> > 
> > Thanks
> > 
> > Goyo
> > 
> > 
> > Sample code -- you need a combination of python shell and matplotlib GUI
> > which allows for interactive use in order to get this working as
> > expected:
> > 
> > ----------------------------------------
> > 
> > from matplotlib import pyplot
> > from matplotlib import dates
> > from datetime import datetime, timedelta
> > from numpy import random
> > 
> > pyplot.ion()
> > 
> > # create data
> > dstart = datetime(2008, 1, 1, 0, 0)
> > dend = datetime(2008, 1, 5, 23, 50)
> > delta = timedelta(minutes=10)
> > x = dates.drange(dstart, dend, delta)
> > y = random.random_sample(len(x))
> > 
> > # plot data
> > pyplot.plot(x, y)
> > 
> > # format x tick labels
> > axis = pyplot.gca()
> > fig = pyplot.gcf()
> > axis.xaxis.set_major_formatter(dates.DateFormatter('%Y-%b-%d %H:%M'))
> > fig.autofmt_xdate()
> > 
> > # draw the figure
> > pyplot.draw()
> > 
> > --------------------------------------
> > 
> > Look at the tick labels, they show both date and time even if you zoom
> > and pan using the GUI.
> > 
> > Now if I want to look at the second day:
> > 
> > dstart = datetime(2008, 1, 1, 0, 0)
> > dend = datetime(2008, 1, 1, 23, 50)
> > pyplot.xlim(dstart, dend)
> > 
> > And the format has changed.
> 
> I don't see this problem using ipython -pylab with mpl from svn on 
> linux, gtkagg backend.  What version, backend, and platform are you using?

matplotlib 0.98.3-3ubuntu1~ppa1 from Benjamin Drung's ppa
(<http://ppa.launchpad.net/bdrung/ubuntu>) on Ubuntu Hardy.

It was the standard python shell and TKAgg, but I get the same result
with ipython -pylab and GTKAgg. Indeed the format change can be
"documented":

print axis.xaxis.get_major_formatter()
pyplot.xlim(dstart, dend)
print axis.xaxis.get_major_formatter()

The first print:
<matplotlib.dates.DateFormatter instance at 0xb6e2462c>
and the second:
<matplotlib.dates.AutoDateFormatter instance at 0x884dc4c>

I did some debugging and realized that xaxis.units is None after
plotting, so xlim triggers a call to xaxis.set_units which sets the
default formatter (and units, whatever it means).

If I set my formatter again, xaxis.units is not None anymore but still
xaxis._update_axisinfo sets the default formatter.

Anyway I worked around this by writing my own version of xlim which
first saves the formatter, then sets xlim and sets the saved formatter
again.

Goyo