Running mlab scripts

Mlab, like the rest of Mayavi, is an interactive application. If you are not already in an interactive environment (see next paragraph), to interact with the figures or the rest of the drawing elements, you need to use the show() function. For instance, if you are writing a script, you need to call show() each time you want to display one or more figures and allow the user to interact with them.

Using mlab interactively

Using IPython_, mlab instructions can be run interactively, or in scripts using IPython_’s %run command:

In [1]: %run my_script

You need to start IPython_ with the –gui=qt option. In this environment, the plotting commands are interactive: they have an immediate effect on the figure, alleviating the need to use the show() function.

Mlab can also be used interactively in the Python shell of the mayavi2 application, or in any interactive Python shell of wxPython-based application (such as other Envisage-based applications, or SPE, Stani’s Python Editor).

Using together with Matplotlib

If you want to use Matplotlib’s interactive plotting with Mayavi’s mlab in IPython you should:

  • start IPython with:

    $ ipython --matplotlib=qt
  • alternatively, start IPython with the –gui=qt option:

    $ ipython --gui=qt

    and before importing any matplotlib modules, enter the following Python commands:

    >>> import matplotlib
    >>> matplotlib.use('Qt4Agg')
    >>> matplotlib.interactive(True)
  • one could also use the --pylab option to IPython as follows:

    $ ipython --pylab=qt

If you want matplotlib and mlab to work together by default in IPython, you can change you default matplotlib backend, by editing the ~/.matplotlib/matplotlibrc to add the following line:

backend     : Qt4Agg

If for some reason, the Qt backend does not work, you can use the wx backend. To do this you may do:

$ ipython --gui=wx

Note that as far as Mayavi is concerned, it chooses the appropriate toolkit using the ETS_TOOLKIT environment variable. If this is not set, the supported toolkits are tried in a version-dependent order until one succeeds. With recent releases of traitsui, the default is Qt. The possible options for ETS_TOOLKIT are:

  • qt4: to use the Qt backend (either PySide or PyQt4),

  • wx: to use wxPython,

  • null: to use no UI toolkit.

In scripts

Mlab commands can be written to a file, to form a script. This script can be loaded in the Mayavi application using the File->Open file menu entry, and executed using the File->Refresh code menu entry or by pressing Control-r. It can also be executed during the start of the Mayavi application using the -x command line switch.

As mentioned above, when running outside of an interactive environment, for instance with python, you need to call the show() function (as shown in the demo above) to pause your script and have the user interact with the figure.

You can also use show() to decorate a function, and have it run in the event-loop, which gives you more flexibility:

from mayavi import mlab
from numpy import random
def image():
   mlab.imshow(random.random((10, 10)))

With this decorator, each time the image function is called, mlab makes sure an interactive environment is running before executing the image function. If an interactive environment is not running, mlab will start one and the image function will not return until it is closed.