15 October 2020

Nuitka Release 0.6.9

This is to inform you about the new stable release of Nuitka. It is the extremely compatible Python compiler, “download now”.

This releases contains important bug fixes for regressions of the 0.6.8 series which had relatively many problems. Not all of these could be addressed as hotfixes, and other issues were even very involved, causing many changes to be necessary.

There are also many general improvements and performance work for tracing and loops, but the full potential of this will not be unlocked with this release yet.

Bug Fixes

  • Fix, loop optimization sometimes didn’t determinate, effectively making Nuitka run forever, with no indication why. This has been fixed and a mechanism to give up after too many attempts has been added.

  • Fix, closure taking object allowed a brief period where the garbage collector was exposed to uninitialized objects. Fixed in already.

  • Python3.6+: Fix corruption for exceptions thrown into asyncgen. Fixed in already.

  • Fix, deleting variables detected as C type bool could raise an UnboundLocalError that was wrong. Fixed in already.

  • Python3.8.3+: Fix, future annotations parsing was using hard coded values that were changed in CPython, leading to errors.

  • Windows: Avoid encoding issues for Python3 on more systems, by going from wide characters to unicode strings more directly, avoiding an encoding as UTF-8 in the middle. Fixed in already.

  • Windows: Do not crash when warning about uninstalled MSVC using Python3. This is a Scons bug that we fixed. Fixed in already.

  • Standalone: The output of dependency walker should be considered as “latin1” rather than UTF-8. Fixed in already.

  • Standalone: Added missing hidden dependencies for flask. Fixed in already.

  • Standalone: Fixed win32com.client on Windows. Fixed in already.

  • Standalone: Use pkgutil to scan encoding modules, properly ignoring the same files as Python does in case of garbage files being there. Fixed in already.

  • Plugins: Enabling a plugin after the filename to compile was given, didn’t allow for arguments to the passed, causing problems. Fixed in already.

  • Standalone: The certifi data file is now supported for all modules using it and not only some.

  • Standalone: The bytecode for the standard library had filenames pointing to the original installation attached. While these were not used, but replaced at run time, they increased the size of the binary, and leaked information.

  • Standalone: The path of sys.executable was not None, but pointing to the original executable, which could also point to some temporary virtualenv directory and therefore not exist, also it was leaking information about the original install.

  • Windows: With the MSVC compiler, elimination of duplicate strings was not active, causing even unused strings to be present in the binary, some of which contained file paths of the Nuitka installation.

  • Standalone: Added support for pyglet.

  • Plugins: The command line handling for Pmw plugin was using wrong defaults, making it include more code than necessary, and to crash if it was not there.

New Features

  • Windows: Added support for using Python 2.7 through a symlink too. This was already working for Python3, but a scons problem prevented this from working.

  • Caching of compiled C files is now checked with ccache and clcache, and added automatically where possible, plus a report of the success is made. This can accelerate the re-compile very much, even if you have to go through Nuitka compilation itself, which is not (yet) cached.

  • Added new --quiet option that will disable informational traces that are going to become more.

  • The Clang from MSVC installation is now picked up for both 32 and 64 bits and follows the new location in latest Visual Studio 2019.

  • Windows: The ccache from Anaconda is now supported as well as the one from msys64.


  • The value tracing has become more correct with loops and in general less often inhibits optimization. Escaping of value traces is now a separate trace state allowing for more appropriate handling of actual unknowns.

  • Memory used for value tracing has been lowered by removing unnecessary states for traces, that we don’t use anymore.

  • Windows: Prevent scons from scanning for MSVC when asked to use MinGW64. This avoids a performance loss doing something that will then end up being unused.

  • Windows: Use function level linking with MSVC, this will allow for smaller binaries to be created, that don’t have to include unused helper functions.


  • The scons file now uses Nuitka utils functions and is itself split up into several modules for enhanced readability.

  • Plugin interfaces for providing extra entry points have been cleaned up and now named tuples are used. Backward compatibility is maintained though.


  • The use of the logging module was replaced with more of our custom tracing and we now have the ability to write the optimization log to a separate file.

  • Old style plugin options are now detected and reported as a usage error rather than unknown plugin.

  • Changed submodules to use git over https, so as to not require ssh which requires a key registered and causes problems with firewalls too.

  • More correct Debian copyright file, made formatting of emails in source code consistent.

  • Added repository for Ubuntu focal.


The main focus of this release has been bug fixes with only a little performance work due to the large amount of regressions and other findings from the last release.

The new constants loading for removes a major scalability problem. The checked and now consistently possible use of ccache and clcache allows for much quicker recompilation. Nuitka itself can still be slow in some cases, but should have seen some improvements too. Scalability will have to remain a focus for the next releases too.

The other focus, was to make the binaries contain no original path location, which is interesting for standalone mode. Nuitka should be very good in this area now.

For optimization, the new loop code is again better. But it was also very time consuming, to redo it, yet again. This has prevented other optimization to be added.

And then for correctness, the locals scope work, while very invasive, was necessary, to handle the usage of locals inside of contractions, but also will be instrumental for function inlining to become generally available.

So, ultimately, this release is a necessary intermediate step. Upcoming releases will be able to focus more clearly on run time performance again as well as on scalability for generated C code.