how to draw one line with different colors

Hi, I'd like to plot my data and indicate where the

    > instrument I used actually actually should truncate
    > those data. My idea is to have y values from zero to a
    > certain maximum and to draw a red line from zero to the
    > lower limit, then to continue with this line colored in
    > black, and finally end this very line colored red from
    > the upper limit to the maximum of my data. How is this
    > to accomplish?

Sorry for the delay in answering this. I am not 100% sure I
understand your question, but it appears to me that you want to color
a line differently depending on it's y value. You can do this with
masked arrays, which are supported in matplotlib CVS

    import as ma
    from matplotlib.numerix import logical_or
    from pylab import plot, show, arange, sin, pi

    t = arange(0.0, 2.0, 0.01)
    s = sin(2*pi*t)

    upper = 0.77
    lower = -0.77

    supper = ma.masked_where(s < upper, s)
    slower = ma.masked_where(s > lower, s)
    smiddle = ma.masked_where(logical_or(s<lower, s>upper), s)

    plot(t, slower, 'r', t, smiddle, 'b', t, supper, 'g')

Another approach, which will work with any recent matplotlib
(including 0.71), is to use a shaded region to indicate your ranges.

    from pylab import plot, show, arange, sin, pi, axhspan

    t = arange(0.0, 2.0, 0.01)
    s = sin(2*pi*t)

    upper = 0.77
    lower = -0.77

    plot(t, s)

    axhspan(upper, 1, facecolor='red', alpha=0.5)
    axhspan(-1, lower, facecolor='blue', alpha=0.5)

    > A second problem for me is probably trivial for more
    > experienced users: How to adjust the size of x- &
    > y-labels (using subplot)?

    > I should mention that I'm stuck with version 0.71 for a
    > while ...

xlabel('my label', fontsize=16)

You can also control the default x and y label size, and the tick
label size, in your rc file

To set the fontsize for the tick labels, you can do something like

  locs, labels = xticks()
  set(labels, fontsize=16)

Should help!