He there,

I'm new to matplotlib but have really been appreciating the thorough documentation and examples online.  I've never worked with matlab either so I'm stumbling  my way around a bit, but have managed to get some basic plots working with my wxPython program.

I'm plotting some simple time/temp curves.  For the time, I have just the number of seconds, starting at 0 and going up to about 1200 (20 minutes).  I'm trying to format the xaxis so that there is a tick mark every one minute, and format the tick marks so they display %M:%S.  The code below doesn't give me *any* formatting or tick marks on the xaxis.  It seems like this should be fairly obvious how to accomplish, but I'm not getting it.

What am I doing wrong here?

xvals = range(1200)
yvals = list of temps

self.mainline = self.ax.plot(xvals, yvals, lw=2, color='red')[0]

locator = matplotlib.dates.MinuteLocator()

formatter = matplotlib.dates.DateFormatter('%M:%S')

# draw the canvas

Any help appreciated...thanks!