Friday, January 22, 2016

PyDev 4.5.3: Debugger fixes and improvements in PyUnit view

PyDev 4.5.3 is now available for download.

This release was done in such a short notice from the last release because a critical issue was fixed in the debugger (although it also added a few improvements to the PyUnit view, making the history dropdown show more information on the run and providing a way to export the results of a run to the clipboard, which are pretty nice).

As a note, LiClipse users (especially those using dark themes) should benefit a lot from the latest release, as it themes the trees and tables scrollbars (with the support from, so, it's a highly recommended download ;)

Anyways, I'll take the chance to talk about the bug which actually triggered this release (which was

The PyDev debugger by default will monkey-patch all the calls which create a new process to automatically connect the debugger to the spawned processes if those are also Python processes -- and it also monkey-patches the os.fork to connect the forked process to the debugger.

Now, in os.fork it always connected the new process to the debugger, as it expected the new process to be a Python process, but there's a catch here: on Linux, subprocess.Popen will first fork the current process and then will do an os.execvp to replace the forked process with a new process, but in the latest version this was making the debugger crash (although it's still not 100% clear to me why that same process wasn't crashing before as the debugger already did this in previous versions -- anyways, os.execvp did some incantation under the hood which crashed when the debugger was setup when it was doing something as subprocess.Popen(['uname', '-m']), which first forked the process, connected it to the debugger and then replaced it with the uname executable).

So, the actual fix was detecting that it was forking for a subprocess.Popen and refrain from setting up the debugger if it was not executing a new Python program ;)


Thursday, January 14, 2016

PyDev 4.5.1: debug faster

PyDev 4.5.1 brings niceties such as an improvement on the code-completion so that properties declared with @property no longer show arguments parenthesis and Ctrl+1 can be used inside a bracketed statement to wrap/unwrap its contents over multiple lines (thanks to yohell). Also, the refactoring, parsing and search had some fixes, but the major changes were in the debugger.

The debugger is much faster and has optional Cython modules for even additional speedups.

In short, the debugger is overall 40% faster without Cython and 138% faster with Cython in the benchmarks created -- although in real world cases I expect even better gains as the benchmarks were done for the cases where the debugger has more overhead than usual.

Graphs with more details on the improvements may be seen at: (performance results with cython). (performance results without cython).

Also, the debugger backend is now also available through "pip install pydevd" (, so, it's easier to setup the remote debugging in a different machine (note that users shouldn't need to install the debugger, only if doing a remote debugging session).

As a note, I'd like to thank JetBrains, which helped on sponsoring the performance improvements in the PyDev Debugger (as it's also the debugger backend used by PyCharm).

For LiClipse users, 2.5.1 (just released too) includes the latest PyDev.