Nuitka Release 0.3.20

This is to inform you about the new stable release of Nuitka. It is the extremely compatible Python compiler. Please see the page "What is Nuitka?" for an overview.

This time there are a few bug fixes and some really major cleanups, lots of new optimization and preparations for more. And then there is a new compiler clang and a new platform supported. MacOS X appears to work mostly, thanks for the patches from Pete Hunt.

Bug fixes

  • The use of a local variable name as an expression was not covered and lead to a compiler crash. Totally amazing, but true, nothing in the test suite of CPython covered this. Issue#30. Fixed in release 0.3.19.1 already.
  • The use of a closure variable name as an expression was not covered as well. And in this case corrupted the reference count. Issue#31. Fixed in release 0.3.19.1 already.
  • The from x import * attempted to respect __all__ but failed to do so. Issue#32. Fixed in release 0.3.19.2 already.
  • The from x import * didn't give a SyntaxError when used on Python3. Fixed in release 0.3.19.2 already.
  • The syntax error messages for "global for function argument name" and "duplicate function argument name" are now identical as well.
  • Parameter values of generator function could cause compilation errors when used in the closure of list contractions. Fixed.

New Features

  • Added support for disabling the console for Windows binaries. Thanks for the patch go to Michael H Kent.
  • Enhanced Python3 support for syntax errors, these are now also compatible.
  • Support for MacOS X was added.
  • Support for using the clang compiler was added, it can be enforced via --clang option. Currently this option is mainly intended to allow testing the "MacOS X" support as good as possible under Linux.

New Optimization

  • Enhanced all optimization that previously worked on "constants" to work on "compile time constants" instead. A "compile time constant" can currently also be any form of a built-in name or exception reference. It is intended to expand this in the future.

  • Added support for built-ins bin, oct, and hex, which also can be computed at compile time, if their arguments are compile time constant.

  • Added support for the iter built-in in both forms, one and two arguments. These cannot be computed at compile time, but now will execute faster.

  • Added support for the next built-in, also in its both forms, one and two arguments. These also cannot be computed at compile time, but now will execute faster as well.

  • Added support for the open built-in in all its form. We intend for future releases to be able to track file opens for including them into the executable if data files.

  • Optimize the __debug__ built-in constant as well. It cannot be assigned, yet code can determine a mode of operation from it, and apparently some code does. When compiling the mode is decided.

  • Optimize the Ellipsis built-in constant as well. It falls in the same category as True, False, None, i.e. names of built-in constants that a singletons.

  • Added support for anonymous built-in references, i.e. built-ins which have names that are not normally accessible. An example is type(None) which is not accessible from anywhere. Other examples of such names are compiled_method_or_function.

    Having these as represented internally, and flagged as "compile time constants", allows the compiler to make more compile time optimization and to generate more efficient C++ code for it that won't e.g. call the type built-in with None as an argument.

  • All built-in names used in the program are now converted to "built-in name references" in a first step. Unsupported built-ins like e.g. zip, for which Nuitka has no own code or understanding yet, remained as "module variables", which made access to them slow, and difficult to recognize.

  • Added optimization for module attributes __file__, __doc__ and __package__ if they are read only. It's the same as __name__.

  • Added optimization for slices and subscripts of "compile time constant" values. These will play a more important role, once value propagation makes them more frequent.

Organizational

  • Created a "change log" from the previous release announcements. It's as ReStructured Text and converted to PDF for the release as well, but I chose not to include that in Debian, because it's so easy to generate the PDF on that yourself.
  • The posting of release announcements is now prepared by a script that converts the ReStructured Text to HTML and adds it to Wordpress as a draft posting or updates it, until it's release time. Simple, sweet and elegant.

Cleanups

  • Split out the nuitka.nodes.Nodes module into many topic nodes, so that there are now nuitka.nodes.BoolNodes or nuitka.nodes.LoopNodes to host nodes of similar kinds, so that it is now cleaner.

  • Split del statements into their own node kind, and use much simpler node structures for them. The following blocks are absolutely the same:

    del a, b.c, d
    
    del a
    del b.c
    del d
    

    So that's now represented in the node tree. And even more complex looking cases, like this one, also the same:

    del a, (b.c, d)
    

    This one gives a different parse tree, but the same bytecode. And so Nuitka need no longer concern itself with this at all, and can remove the tuple from the parse tree immediately. That makes them easy to handle. As you may have noted already, it also means, there is no way to enforce that two things are deleted or none at all.

  • Turned the function and class builder statements into mere assignment statements, where defaults and base classes are handled by wrapping expressions.

    Previously they are also kind of assignment statements too, which is not needed. Now they were reduced to only handle the bases for classes and the defaults for functions and make optional.

  • Refactored the decorator handling to the tree building stage, presenting them as function calls on "function body expression" or class body expression".

    This allowed to remove the special code for decorators from code generation and C++ templates, making decorations easy subjects for future optimization, as they practically are now just function calls.

    @some_classdecorator
    class C:
        @staticmethod
        def f():
            pass
    

    It's just a different form of writing things. Nothing requires the implementation of decorators, it's just functions calls with function bodies before the assignment.

    The following is only similar:

    class C:
        def f():
            pass
    
        f = staticmethod(f)
    
    C = some_classdecorator(C)
    

    It's only similar, because the assignment to an intermediate value of C and f is not done, and if an exception was raised by the decoration, that name could persist. For Nuitka, the function and class body, before having a name, are an expression, and so can of course be passed to decorators already.

  • The in-place assignments statements are now handled using temporary variable blocks

    Adding support for scoped temporary variables and references to them, it was possible to re-formulate in-place assignments expressions as normal look-ups, in-place operation call and then assignment statement. This allowed to remove static templates and will yield even better generated code in the future.

  • The for loop used to have has a "source" expression as child, and the iterator over it was only taken at the code generation level, so that step was therefore invisible to optimization. Moved it to tree building stage instead, where optimization can work on it then.

  • Tree building now generally allows statement sequences to be None everywhere, and pass statements are immediately eliminated from them immediately. Empty statement sequences are now forbidden to exist.

  • Moved the optimization for __name__ to compute node of variable references, where it doesn't need anything complex to replace with the constant value if it's only read.

  • Added new bases classes and mix-in classes dedicated to expressions, giving a place for some defaults.

  • Made the built-in code more reusable.

New Tests

  • Added some more diagnostic tests about complex assignment and del statements.
  • Added syntax test for star import on function level, that must fail on Python3.
  • Added syntax test for duplicate argument name.
  • Added syntax test for global on a function argument name.

Summary

The decorator and building changes, the assignment changes, and the node cleanups are all very important progress for the type inference work, because they remove special casing the that previously would have been required. Lambdas and functions now really are the same thing right after tree building. The in-place assignments are now merely done using standard assignment code, the built functions and classes are now assigned to names in assignment statements, much more consistency there.

Yet, even more work will be needed in the same direction. There may e.g. be work required to cover with statements as well. And assignments will become no more complex than unpacking from a temporary variable.

For this release, there is only minimal progress on the Python3 front, despite the syntax support, which is only miniscule progress. The remaining tasks appear all more or less difficult work that I don't want to touch now.

There are still remaining steps, but we can foresee that a release may be done that finally actually does type inference and becomes the effective Python compiler this project is all about.

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