FAQ

There are a number of questions that repeatedly need to be answered. The following document tries to answer some of them.

Technical FAQ

Fatal Python error: (pygame parachute) Segmentation Fault

Most of time, this issue is due to an usage of old graphics driver. Install the latest graphics driver available for your graphics card, and it could be ok.

if not, please report a detailed issue on github by following the instructions in the Reporting an Issue section of the Contributing documentation. This is very important for us because that kind of error can be very hard to debug. Give us all the informations you can give about your environment and execution.

undefined symbol: glGenerateMipmap

You might have a too old graphics card. Update your graphics drivers to the latest available version, and retry.

ImportError: No module named event

If you use Kivy from our development version, you must compile it before using it. In the kivy directory, do:

make force

Pip installation failed

Installing Kivy using Pip is not currently supported. Because Pip force the usage of setuptools, setuptools hack build_ext to use pyrex for generating .c, and they are no clean solution to hack against both weird behaviors to use Cython. (Reference: http://mail.scipy.org/pipermail/nipy-devel/2011-March/005709.html)

Solution: use easy_install, as our documentation said.

Android FAQ

could not extract public data

This message error can happen in many cases. Ensure that:

  • you have a phone with sdcard
  • you are not currently in a “USB Mass Storage” mode
  • you have the permissions to write on sdcard

In case of USB Mass Storage mode error, and if you don’t want to keep unplugging the device, set the usb option to Power.

Is it possible to have a kiosk app on android 3.0 ?

Thomas Hansen have wrote a detailed answer on kivy-users mailing list:

Basicaly, you need to root de device, remove the SystemUI package, add some line on the xml configuration, and you’re done.

Project FAQ

Why do you use Python? Isn’t it slow?

Let us try to give a thorough answer; please bear with us.

Python is a very agile language that allows you to do many things in (by comparison) short time. For many development scenarios, we strongly prefer writing our application quickly in a high-level language such as Python, testing it, then optionally optimizing it.

But what about speed? If you compare execution speeds of implementations for a certain set of algorithms (esp. number crunching) you will find that Python is a lot slower than say, C++. Now you may be even more convinced that it’s not a good idea in our case to use Python. Drawing sophisticated graphics (and we are not talking about your grandmother’s OpenGL here) is computationally quite expensive and given that we often want to do that for rich user experiences, that would be a fair argument. But, in virtually every case your application ends up spending most of the time (by far) executing the same part of the code. For Kivy for example, these parts are event dispatching and graphics drawing. Now Python allows you to do something to make these parts much faster.

By using Cython, you can compile your code down to the C level, and from there your usual C compiler optimizes things. This is a pretty pain free process and if you add some hints to your code, the result becomes even faster. We are talking about a speed up in performance by a factor of anything in between 1x and up to more than 1000x (greatly depends on your code). In Kivy, we did this for you and implemented the portions of our code where efficiency really is critical on the C level.

For graphics drawing, we also leverage today’s GPUs which are, for some tasks such as graphics rasterization, much more efficent than a CPU. Kivy does as much as is reasonable on the GPU to maximize performance. If you use our Canvas API to do the drawing, there is even a compiler that we invented which optimizes your drawing code automatically. If you keep your drawing on the GPU mostly, much of your program’s execution speed is not determined by the programming language used, but by the graphics hardware you throw at it.

We believe that these (and other) optimizations that Kivy does for you already make most applications fast enough by far. Often you will even want to limit the speed of the application in order not to waste resources. But even if this is not sufficient, you still have the option of using Cython for your own code to greatly speed it up.

Trust us when we say that we have given this very careful thought. We have performed many different benchmarks and came up with quite some clever optimizations to make your application run smoothly.

Does Kivy support Python 3.x?

No. Not yet. Python 3 is certainly a good thing; However, it broke backwards compatibility (for good reasons) which means that some considerable portion of available Python projects do not yet work with Python 3. This also applies to some of the projects that Kivy can use as a dependency, which is why we didn’t make the switch yet. We would also need to switch our own codebase to Python 3. We didn’t do that yet because it’s not very high on our priority list, but if somebody doesn’t want to wait for us doing it, please go ahead. Please note, though, that Python 2.x is still the de facto standard.

Do you accept patches?

Yes, we love patches. In order to ensure a smooth integration of your precious changes, however, please make sure to read our contribution guidelines. Obviously we don’t accept every patch. Your patch has to be coherent with our styleguide and, more importantly, make sense. It does make sense to talk to us before you come up with bigger changes, especially new features.

Does the Kivy project participate in Google’s Summer of Code 2012?

Since Google announced that there will be a GSoC 2012 we have had many potential students ask whether we would participate. The clear answer is: Indeed. :-) The NUIGroup has applied as an umbrella organization and luckily got chosen as one of the mentoring organizations. Given enough slots for NUIGroup, slots will be dedicated to Kivy. That also depends on the overall quality of the student proposals (i.e. if there is only one Kivy student proposal with a bad quality, Kivy will not get a slot). If you want to participate as a student and want to maximize your chances of being accepted, start talking to us today and try fixing some smaller (or larger, if you can ;-) problems to get used to our workflow. If we know you can work well with us, that’d be a big plus.

See: http://gsoc.nuigc.com/

Here’s a checklist:

  • Make sure to read through the website and at least skim the documentation.
  • Look at the source code.
  • Read our contribution guidelines.
  • Pick an idea that you think is interesting from the ideas list (see link above) or come up with your own idea.
  • Do some research yourself. GSoC is not about us teaching you something and you getting paid for that. It is about you trying to achieve agreed upon goals by yourself with our support. The main driving force in this should be, obviously, yourself, though. Many students come up and ask what they should do. Well, we don’t know because we know neither your interests nor your skills. Show us you’re serious about it and take initiative.
  • Write a draft proposal about what you want to do. Include what you understand the current state is (very roughly), what you would like to improve and how, etc.
  • Discuss that proposal with us in a timely manner. Get feedback.
  • Be patient! Especially on IRC. We will try to get to you if we’re available. If not, send an email and just wait. Most questions are already answered in the docs or somewhere else and can be found with some research. If your questions don’t reflect that you’ve actually thought through what you’re asking, that might not be received well.

Good luck! :-)