Oct 11, 2013

Distributing Pure Python ROS Applications

In June 2013 I was lucky to speak at the fantastic SciPy2013 conference (scientific computing with python). I spoke about a work flow and tools we have developed at strawlab. The title of my talk was Managing Complex Experiments, Automation, and Analysis using Robot Operating System. The video of that talk is included below;

And here are the accompanying slides;

This post describes a tool I developed for distributing ROS packages to scientific collaborators. That software is called ros-freeze.

For those of you not aware, ROS is a great framework traditionally targeted for robotics but usable in other fields too. In particular it has a relatively good performance and simple, strongly typed, inter-process-communication framework and serialization format. This is simultaneously useful for creating distributed realtime-ish systems with comprehensive logging of the system state. Best of all, the python interface to ROS is very clean.


Unfortunately, being a framework, ROS is rather all-or-nothing (going as far as to describe itself as a meta-operating system). The basic ROS install is several gigabytes, and building it yourself can be rather difficult. Furthermore, as I mentioned in my presentation, it is attractive to use the built in ROS tool rosbag for recording timestamped data to disk. Unfortunately, reading these files again needs ROS, thus necessarily coupling experimental data to the software used to collect it.

To remedy this I wrote ros-freeze, a python tool to convert any ROS package into a pure-python package including all of the dependencies. Collaborators can then install the python package and immediately have access to all the same ROS packages and libraries without having to build the whole ROS stack.

Converting your ROS package

  1. Download ros-freeze from here

  2. Modify setup-freeze.py according to your needs

    from setuptools import setup
    from rosfreeze import import_ros_package, get_disutils_cmds
    MY_PACKAGE = 'foo'
    setup(name='python-ros-%s' % MY_PACKAGE,
          description='Pure Python ROS %s' % MY_PACKAGE,
          **get_disutils_cmds(srcdir, bindir, datadir)
  3. Build a python egg (for example)

    $ python setup-freeze.py bdist_egg

  4. Install that egg into your virtual environment

Caveats and other Notes

  • this is currently working on ROS Electric (an old release, at work we have chosen to stick with Ubuntu 12.04LTS)
  • changes for other ROS distributions might be necessary, so please get in touch
  • this is successfully tested on ROS packages containing tens of thousands of lines of code and dozens of ROS dependencies.
  • although recent ROS releases have improved the package management situation (by embracing deb packaging, yay!) this tool provides an unprecedentedly easy way to distribute your pure python ROS applications

A Pure Python ROS Distribution?

One side effect of this was the packaging of the pure python ROS core as an easily installable python egg. This means that you can write, debug and test python ROS nodes without having to install the whole ROS distribution.

One can even go as far as running rosmaster and the command line tools (rosnode, rosparam, etc)!

You can download the python-ros-electric package from here.

Sep 29, 2013

Lightweight Development Prefixes

Lately I have been writing a lot of native code against multiple OpenCV versions. Like many Linux developers I tend to keep different development prefixes isolated using LD_LIBRARY_PATH (and friends).

I recently took the time to clean up a little script I use for this purpose, and posted it online. Inspired by virtualenv, it now has a prompt!


To use the script:

  1. create the development directory
  2. copy the script there
  3. source /path/to/env.sh

please leave comments or suggestions on the gist.

Sep 24, 2013

GNOME Tweak Tool 3.10 Improvements

In collaboration with GSOC student Alex Muñoz and designer Allan Day, GNOME Tweak Tool has seen many improvements this cycle, both 'under the hood', and most noticeably, in the form of a modern GNOME3 UI design. The difference is stark; compare the old and the new versions below;

New UI

Old UI

In addition to the use of new widgets (Gtk.HeaderBar, Gtk.Application, Gtk.Stack, Gtk.SearchBar) the organisation of tweaks into categories has been updated. This should make many settings easier to find, especially in conjunction with new translations for many tweak names and descriptions.

Historically, the tweak tool UI was mostly auto-generated, resulting in a rather uniform and boring look, and more importantly the inability to easily group tweaks together to show causality (such as turning off desktop icons makes the options to show specific types of icons on the desktop redundant). This architectural limitation has now been fixed, and in addition, specialized UI elements have been created for certain tweaks; startup applications, shell extensions, desktop icons, the shell top bar, etc.

Desktop Icon Options

Other highlights of 3.10 include;

  • Allow updating GNOME Shell extensions from inside tweak tool
  • Startup application management
  • Offer to logout user when tweaks require the session restarted
  • GNOME style sidebar and search
  • Ability to disable middle-click paste (great for designers!)
  • Show text in tooltip when label is ellipsized, and make window maximizable and resizable.
  • Better tweak names and descriptions (manage our own translations instead of getting all from gsettings)

Startup Applications

Unfortunately, not all features I wanted to implement were completed. Things I will be working on in 3.12 include;

  • Hidpi tweak (this will land in 3.10.1)
  • Better search interaction (focus stealing and search-results layout fixes)
  • Improved layout when the window is maximized
  • Resurrect the wacom panel (this was generously contributed at the start of the cycle, but I had no time to port it to the new design, nor any way to test it)
  • Privileged helper for operations requiring root permissions (power management options, installing system wide themes)
  • Keyboard layout specialized UI
  • Theme management UI

For more information on GNOME 3.10 and GNOME Tweak Tool 3.10 check out world of gnome here, here, and here again, and wiki.gnome.org. Hope you all enjoy the release.

Feb 3, 2013

Python Bindings to the Pointcloud Library

I'd like to announce the release of python-pcl, python bindings to the pointcloud library.

This is not a full binding to the rather large PCL API. Currently, the following parts of the API are wrapped

  • I/O and integration; saving and loading PCD files
  • segmentation
  • sample consensus model fittting (RANSAC + others, cylinders, planes, common geometry)
  • smoothing
  • filtering

The code tries to follow the Point Cloud API, and also provides helper function for interacting with numpy.

A minimal example (demonstrating the StatisticalOutlierFilter

import pcl

p = pcl.PointCloud()

fil = p.make_statistical_outlier_filter()
fil.set_mean_k (50)
fil.set_std_dev_mul_thresh (1.0)


Filtering Example

The main limitation of the current implementation is that is only supports the PointXYZ point type. PCL is a heavily optimized and templated API, and the best method for creating specializations correspoinding to the correct point type in a dynamic language like Python is not clear.

Nevertheless, the binding is already capable of smoothing, filtering and the fitting of geometries in arbitary 3D point cloud data.

The binding is written using Cython, and is one of the more complex C++ bindings I could find.

The current release has been tested with

  • pcl 1.5.1
  • Cython 0.16

although it should work with more recent releases.

I would be interested in adressing the specialization issues using the recently added and improved fused types support in Cython.

This work has been supported by, and is currently in production use at, Strawlab.

Jan 27, 2013

ROS and Gtk for Laboratory Control

At the lab in which I work (Andrew Straw, strawlab) we study the visual flight behaviour of Drosophila using virtual reality. The implementation of this will be explained in future posts and papers however for this post I am going to describe how I used Gtk1 and ROS to build an interface to control and monitor running experiments (called the 'Operator Console').

A future post will address and release all the ROS+GObject2 glue that lets these interfaces scale dynamically as nodes (dis)appear. This just shows the relevant Gtk parts and has some comments on what I would like from Gtk to make these sort of interfaces easier.

The screenshow shows the first tab of the 'Operator Console'3.

Operator Console

Implementation Notes

  • I use the secondary icon support of Gtk.Entry to show the contents contain sensible data. Maybe validation support in Gtk would be useful here bug.
  • The 'Description' entry is a Gtk.TextView, not a Gtk.Entry. It was necessary to apply custom CSS to make it look reasonably similar. Sadly, it does not support the full/same set of CSS properties as Gtk.Entry, so it was impossible to show the same border radius and focus colors bug. Perhaps a multi-line Gtk.Entry would be better.
  • The bottom half of the window shows the utilisation of all computers. I tried a few versions of this, and simple sensibly formatted monospaced text looked much better than anything else I tried. Any suggestions?

This screenshot shows an example screen where we mix the control and monitoring or many instances of the same ROS node.

Operator Console

Implementation Notes

  • The Gtk.Switch simultainously displays the status of the projector, and also allows control of the node. The is a common use-case in the software, and due to the asynchronous nature of the ROS messages, I need to distinguish these from user-generated signals. I have wrappers such as the following for many widgets4. Advice on how to distinguish this use-case would be preferred.
class UpdateableGtkSwitch(Gtk.Switch):
    def __init__(self, *args, **kwargs):
        Gtk.Switch.__init__(self, *args, **kwargs)
        self._changing = False
        self.connect_after("notify::active", self._changed)

    def _changed(self, *args):
        if self._changing:

    def set_active(self, is_active):
        self._changing = True
        Gtk.Switch.set_active(self, is_active)
        self._changing = False

    def connect(self, *args, **kwargs):
        self.connect_after(*args, **kwargs)
  • The "Standby (Computer1)" is for display only and mirrors the status of a ROS topic. I would like some way visually to inicate that this widget is not actually an editable Gtk.Entry. Currently the Gtk.Entry is set editable = False, it looks to out of place with sensitive = False. Perhaps I should add some custom CSS to color it slightly different. Suggestions are appreciated.

Closing Remarks

I'm really happy with the status of the PyGObject bindings. We have a few quite large applications built using them (and ROS) and I have no complaints about performance5 or otherwise. The conventional wisdom was that PyGTK (and GTK) were not suitable for threaded workloads but the threading model of ROS guarentees that the 'operator-console' shown above manages upwards of 50 background threads asynchronously updating the GUI state.

  1. Actually PyGObject, argh why didn't we keep the name as pygtk? 

  2. I'll blog about this later. For the curious, rosgobject lives here. 

  3. In real operation this GUI shows the state of many more machines/nodes/computers. This screenshot is running on my laptop because showing too much more might give away the game ;-). 

  4. freeze_notify and thaw_notify would almost work, if the events could be dropped and not queued. Also, not all widgets use notify::active, GtkComboBox(Text) for example. A general way to do this would be preferred. 

  5. Excluding plotting / graphing performace. But that is fodder for a later post. 

Jul 27, 2012


An organised person would have blogged about going to GUADEC before the event started. I am not that person. I am there now. Come see me if you want to talk about / hack on

  • GNOME tweak tool

  • Scientific computing with PyGObject (improving interaction with numpy, etc)

  • Windows builds of PyGObject + GTK3

  • Real time charting (https://github.com/nzjrs/uber-graph)

Oct 19, 2011

A Change

2011 has been an interesting year. Between the stupid earthquakes and the pressure of finishing my PhD, I have been silent because I have had nothing interesting to talk about (cf. twitter...).

But there is a light at the end, I'm on track to complete my thesis, 'Biologically Inspired Visual Control of Flying Robots', in December/January.

Christchurch, demolished, the old...

I'm excited to say that I have accepted a job at the Institute of Molecular pathology, in a research group studying the mechanisms of visual flight control in insects. Technology wise, it is a perfect fit; the experimental apparatus involves a multi-camera real-time flight tracking system and estimator for multiple targets in an augmented reality flight arena. It is open-source (ish), and python/numpy. Research wise, it allows me to investigate some of the assumptions and unknowns in the biomimetic control systems I implemented during my PhD. And it is in Vienna, 1st Feb, 2012!

Vienna, the new...

This is a career change for me. In the last few years it became increasingly clear that I was morally uncomfortable with the use of UAVs as weapons (drones). Previously I had consoled myself with there existing an ethical and philosophical difference between 'the application of research' and 'the action of research'. When It came to looking for work, and considering who to work for, this difference was often eroded.

It has also been particularly frustrating being in New Zealand for the last 12 months and watching our flaccid national response to the three recent challenges here (world cupearthquakerena oil spill).

Technology Tidbits

This post has been brought to you by procrastination.

Jul 15, 2011

Interfacing Python + C + OpenCV via ctypes

I was recently asked to help a colleague access his image processing C-library from python; quite a common task. As those of you who are familiar with Python might realise, there are a whole bag of ways that this can be accomplished;

In this case the colleague only needed to access a single function from the library returning image data, and then hand this result onto OpenCV. One happy side effect of the new (> v2.1) python-opencv bindings is that they do no validation on CvImage.SetData, which means you can pass an arbitrary string/pointer. Because of this I advised him I thought using something like SWIG was overkill, and he could just write a wrapper to his library using ctypes, or a thin python extension directly.

Image data contains embedded NULLs, and I could not find a concise example of dealing with non null-terminated, non-string char * arrays via ctypes so I wrote one.

# char *test_get_data_nulls(int *len);

func = lib.test_get_data_nulls
func.restype = POINTER(c_char)
func.argtypes = [POINTER(c_int)]

l = c_int()
data = func(byref(l))

print data,l,data.contents

and, another approach

# void test_get_data_nulls_out(char **data, int *len);

func_out = lib.test_get_data_nulls_out
func_out.argtypes = [POINTER(POINTER(c_char)), POINTER(c_int)]
func.restype = None

l2 = c_int()
data2 = POINTER(c_char)()
func_out(byref(data2), byref(l2))

print data2,l2,data2.contents

The full code can be found here and contains examples showing how to deal with data of this type using ctypes, and by writing a simple python extension linking with the library in question.

Apr 3, 2011

End of an Era: PyGTK

I just released PyGTK 2.24, which will almost certainly be the last major PyGTK release. The future of Python on the GNOME platform is PyGObject + GObject Introspection. From my experience over the last few months porting a number of my projects, the future is bright.

In a cruel twist of irony, the state of PyGTK on Windows and Mac has never been better. The credit for the windows work (and some great documentation improvements this cycle) must go to Dieter Verfaillie

I hope that the new stack will reach the same level of capability on other platforms as GTK+ 2.24, but in the large scheme of things the renewed development excitement surrounding GTK+ 3.0 and GNOME 3 is excellent consolation.

As a user I would like to thank those developers before me for creating PyGTK. It was the first 'pythonic' UI toolkit for linux, and a pleasure to use. As the recent maintainer of PyGTK I would especially like to thank those recent developers who helped me, in particular Dieter Verfaillie who really pushed PyGTK over the line regarding Windows support, into the great state it is now.

I'll leave you with some graphical statistics (generated using pepper) for the 12 year history of PyGTK. If planet strips the wordpress gallery then please click here.







update: To clarify a point raised in the comments, PyGTK will be maintained in the exact same was as the GTK+-2.0 series will be maintained. Bug fix releases will be made if necessary, but no new features will be added. If you want the new GTK+-3.0 features then you should use PyGObject + GObject Introspection.

The PyGTK code will not disappear from any servers, it will continue to be shipped in all distributions for the forseeable future, it will continue to work very well on windows, and many applications will continue to use it.

Dec 24, 2010

PyGTK All-in-one Installer for Windows

The PyGTK team is pleased to announce the return of the highly popular all-in-one installer for Windows.

The PyGTK All-in-one installer provides an alternative installation method for PyGTK users on Windows. It bundles PyGTK, PyGObject, PyCairo, PyGtkSourceView2, PyGooCanvas, PyRsvg, the gtk+-bundle and Glade in one handy installer.

Currently 32 bit Python 2.6 and 2.7 versions are supported on Windows XP and above.

Dieter Verfaillie deserves enormous thanks for this work. Firstly, he performed the tedious job of ensuring that all the component MSI installers were exactly correct, and secondly, the really difficult task of deconstructing these individual installers and reassembling their contents into a single cohesive executable.

This is a true all-in-one installer, it does not simply call out to launch the individual MSI files.

  • More screenshots here.

  • Please file bugs as appropriate.

  • We are looking to collaborate with others who want to create gtk+ (and friends) all-in-one installers for Windows. We anticipate the tools to generate these installers will move to GNOME in future - perhaps in a common repository. Suggestions and feedback welcome.

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