25 January 2017

Nuitka Release 0.5.25

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

This release contains a huge amount of bug fixes, lots of optimization gains, and many new features. It also presents many organizational improvements, and many cleanups.

Bug Fixes

  • Python3.5: Coroutine methods using super were crashing the compiler. Fixed in already.

  • Python3.3: Generator return values were not properly transmitted in case of tuple or StopIteration values.

  • Python3.5: Better interoperability between compiled coroutines and uncompiled generator coroutines.

  • Python3.5: Added support to compile in Python debug mode under Windows too.

  • Generators with arguments were using two code objects, one with, and one without the CO_NOFREE flag, one for the generator object creating function, and one for the generator object.

  • Python3.5: The duplicate code objects for generators with arguments lead to interoperability issues with between such compiled generator coroutines and compiled coroutines. Fixed in already.

  • Standalone: On some Linux variants, e.g. Debian Stretch and Gentoo, the linker needs more flags to really compile to a binary with RPATH.

  • Compatibility: For set literal values, insertion order is wrong on some versions of Python, we now detect the bug and emulate it if necessary, previous Nuitka was always correct, but incompatible.

    {1, 1.0}.pop()  # the only element of the set should be 1
  • Windows: Make the batch files detect where they live at run time, instead of during setup.py, making it possible to use them for all cases.

  • Standalone: Added package paths to DLL scan for depends.exe, as with wheels there now sometimes live important DLLs too.

  • Fix, the clang mode was regressed and didn’t work anymore, breaking the macOS support entirely.

  • Compatibility: For imports, we were passing for locals argument a real dictionary with actual values. That is not what CPython does, so stopped doing it.

  • Fix, for raised exceptions not passing the validity tests, they could be used after free, causing crashes.

  • Fix, the environment CC wasn’t working unless also specifying CXX.

  • Windows: The value of __file__ in module mode was wrong, and didn’t point to the compiled module.

  • Windows: Better support for --python-debug for installations that have both variants, it is now possible to switch to the right variant.

New Features

  • Added parsing for shebang to Nuitka. When compiling an executable, now Nuitka will check of the #! portion indicates a different Python version and ask the user to clarify with --python-version in case of a mismatch.

  • Added support for Python flag --python-flag=-O, which allows to disable assertions and remove doc strings.


  • Faster method calls, combining attribute lookup and method call into one, where order of evaluation with arguments doesn’t matter. This gives really huge relative speedups for method calls with no arguments.

  • Faster attribute lookup in general for object descendants, which is all new style classes, and all built-in types.

  • Added dedicated xrange built-in implementation for Python2 and range for Python3. This makes those faster while also solving ordering problems when creating constants of these types.

  • Faster sum again, using quick iteration interface and specialized quick iteration code for typical standard type containers, tuple and list.

  • Compiled generators were making sure StopIteration was set after their iteration, although most users were only going to clear it. Now only the send method, which really needs that does it. This speed up the closing of generators quite a bit.

  • Compiled generators were preparing a throw into non-started compilers, to be checked for immediately after their start. This is now handled in a generic way for all generators, saving code and execution time in the normal case.

  • Compiled generators were applying checks only useful for manual send calls even during iteration, slowing them down.

  • Compiled generators could duplicate code objects due to handling a flag for closure variables differently.

  • For compiled frames, the f_trace is not writable, but was taking and releasing references to what must be None, which is not useful.

  • Not passing locals to import calls make it less code and faster too.


  • This release also prepares Python 3.6 support, it includes full language support on the level of CPython 3.6.0 with the sole exception of the new generator coroutines.

  • The improved mode is now the default, and full compatibility is now the option, used by test suites. For syntax errors, improved mode is always used, and for test suites, now only the error message is compared, but not call stack or caret positioning anymore.

  • Removed long deprecated option “–no-optimization”. Code generation too frequently depends on not seeing unoptimized code. This has been hidden and broken long enough to finally remove it.

  • Added support for Python3.5 numbers to Speedcenter. There are now also tags for speedcenter, indicating how well “develop” branch fares in comparison to the stable branch.

  • With a new tool, source code and Developer Manual contents can be kept in sync, so that descriptions can be quoted there. Eventually a full Sphinx documentation might become available, but for now this makes it workable.

  • Added repository for Ubuntu Yakkety (16.10) for download.

  • Added repository for Fedora 25 for download.


  • Moved the tools to compare CPython output, to sort import statements (isort) to auto-format the source code (Redbaron usage), and to check with PyLint to a common new nuitka.tools package, runnable with __main__ modules and dedicated runners in bin directory.

  • The tools now share code to find source files, or have it for the first time, and other things, e.g. finding needed binaries on Windows installations.

  • No longer patch traceback objects dealloc function. Should not be needed anymore, and most probably was only bug hiding.

  • Moved handling of ast nodes related to import handling to the proper reformulation module.

  • Moved statement generation code to helpers module, making it accessible without cyclic dependencies that require local imports.

  • Removed deprecated method for getting constant code objects in favor of the new way of doing it. Both methods were still used, making it harder to analyse.

  • Removed useless temporary variable initializations from complex call helper internal functions. They worked around code generation issues that have long been solved.

  • The ABI flags are no longer passed to Scons together with the version.


  • Windows: Added support to detect and to switch debug Python where available to also be able to execute reference counting tests.

  • Added the CPython 3.3 test suite, after cleaning up the worst bits of it, and added the brandnew 3.6 test suite with a minimal set of changes.

  • Use the original 3.4 test suite instead of the one that comes from Debian as it has patched quite a few issues that never made it upstream, and might cause crashes.

  • More construct tests, making a difference between old style classes, which have instances and new style classes, with their objects.

  • It is now possible to run a test program with Python3 and Valgrind.


The quick iteration is a precursor to generally faster iteration over unknown object iterables. Expanding this to general code generation, and not just the sum built-in, might yield significant gains for normal code in the future, once we do code generation based on type inference.

The faster method calls complete work that was already prepared in this domain and also will be expanded to more types than compiled functions. More work will be needed to round this up.

Adding support for 3.6.0 in the early stages of its release, made sure we pretty much have support for it ready right after release. This is always a huge amount of work, and it’s good to catch up.

This release is again a significant improvement in performance, and is very important to clean up open ends. Now the focus of coming releases will now be on both structural optimization, e.g. taking advantage of the iterator tracing, and specialized code generation, e.g. for those iterations really necessary to use quick iteration code.