[Cython] Cython 0.21 released

Stefan Behnel stefan_ml at behnel.de
Wed Sep 10 18:40:37 CEST 2014

Hi all,

on behalf of the Cython dev team, I'm pleased to announce the release of
Cython 0.21, a major feature release. Thanks everyone who contributed code,
documentation improvements, test feedback, bug reports and/or otherwise
helpful insights for this release.

I copied the complete changelog of this release below, but here are the
major highlights, in addition to the many bug fixes and general
improvements in this release.

* Legacy code and support for old CPython versions was removed, baselines
are now Python 2.6 and 3.2.

* cdef functions finally support inner Python functions with closures.

* C enums can now be declared as "cpdef" to publish them to Python space.

* Python method calls, boolean "and/or" operators and cascaded assignments
were optimised to streamline calls and type coercions.

* The annotated HTML code output is syntax highlighted and beautified.

Have fun,








0.21 (2014-09-10)

Features added

* C (cdef) functions allow inner Python functions.

* Enums can now be declared as cpdef to export their values to
  the module's Python namespace.  Cpdef enums in pxd files export
  their values to their own module, iff it exists.

* Allow @staticmethod decorator to declare static cdef methods.
  This is especially useful for declaring "constructors" for
  cdef classes that can take non-Python arguments.

* Taking a ``char*`` from a temporary Python string object is safer
  in more cases and can be done inside of non-trivial expressions,
  including arguments of a function call.  A compile time error
  is raised only when such a pointer is assigned to a variable and
  would thus exceed the lifetime of the string itself.

* Generators have new properties ``__name__`` and ``__qualname__``
  that provide the plain/qualified name of the generator function
  (following CPython 3.5).  See http://bugs.python.org/issue21205

* The ``inline`` function modifier is available as a decorator
  ``@cython.inline`` in pure mode.

* When cygdb is run in a virtualenv, it enables the same virtualenv
  inside of the debugger. Patch by Marc Abramowitz.

* PEP 465: dedicated infix operator for matrix multiplication (A @ B).

* HTML output of annotated code uses Pygments for code highlighting
  and generally received a major overhaul by Matthias Bussonier.

* IPython magic support is now available directly from Cython with
  the command "%load_ext cython".  Cython code can directly be
  executed in a cell when marked with "%%cython".  Code analysis
  is available with "%%cython -a".  Patch by Martín Gaitán.

* Simple support for declaring Python object types in Python signature
  annotations.  Currently requires setting the compiler directive

* New directive ``use_switch`` (defaults to True) to optionally disable
  the optimization of chained if statement to C switch statements.

* Defines dynamic_cast et al. in ``libcpp.cast`` and C++ heap data
  structure operations in ``libcpp.algorithm``.

* Shipped header declarations in ``posix.*`` were extended to cover
  more of the POSIX API.  Patches by Lars Buitinck and Mark Peek.


* Simple calls to C implemented Python functions/methods are faster.
  This also speeds up many operations on builtins that Cython cannot
  otherwise optimise.

* The "and"/"or" operators try to avoid unnecessary coercions of their
  arguments.  They now evaluate the truth value of each argument
  independently and only coerce the final result of the whole expression
  to the target type (e.g. the type on the left side of an assignment).
  This also avoids reference counting overhead for Python values during
  evaluation and generally improves the code flow in the generated C code.

* The Python expression "2 ** N" is optimised into bit shifting.
  See http://bugs.python.org/issue21420

* Cascaded assignments (a = b = ...) try to minimise the number of
  type coercions.

* Calls to ``slice()`` are translated to a straight C-API call.

Bugs fixed

* Crash when assigning memory views from ternary conditional expressions.

* Nested C++ templates could lead to unseparated ">>" characters being
  generated into the C++ declarations, which older C++ compilers could
  not parse.

* Sending SIGINT (Ctrl-C) during parallel cythonize() builds could
  hang the child processes.

* No longer ignore local setup.cfg files for distutils in pyximport.
  Patch by Martin Teichmann.

* Taking a ``char*`` from an indexed Python string generated unsafe
  reference counting code.

* Set literals now create all of their items before trying to add them
  to the set, following the behaviour in CPython.  This makes a
  difference in the rare case that the item creation has side effects
  and some items are not hashable (or if hashing them has side effects,

* Cython no longer generates the cross product of C functions for code
  that uses memory views of fused types in function signatures (e.g.
  ``cdef func(floating[:] a, floating[:] b)``).  This is considered the
  expected behaviour by most users and was previously inconsistent with
  other structured types like C arrays.  Code that really wants all type
  combinations can create the same fused memoryview type under different
  names and use those in the signature to make it clear which types are

* Names that were unknown at compile time were looked up as builtins at
  runtime but not as global module names.  Trying both lookups helps with
  globals() manipulation.

* Fixed stl container conversion for typedef element types.

* ``obj.pop(x)`` truncated large C integer values of x to ``Py_ssize_t``.

* ``__init__.pyc`` is recognised as marking a package directory
  (in addition to .py, .pyx and .pxd).

* Syntax highlighting in ``cython-mode.el`` for Emacs no longer
  incorrectly highlights keywords found as part of longer names.

* Correctly handle ``from cython.submodule cimport name``.

* Fix infinite recursion when using super with cpdef methods.

* No-args ``dir()`` was not guaranteed to return a sorted list.

Other changes

* The header line in the generated C files no longer contains the
  timestamp but only the Cython version that wrote it.  This was
  changed to make builds more reproducible.

* Removed support for CPython 2.4, 2.5 and 3.1.

* The licensing implications on the generated code were clarified
  to avoid legal constraints for users.

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