=================
Features added
--------------
* Cdef classes can now multiply inherit from ordinary Python classes.
(The primary base must still be a c class, possibly ``object``, and
the other bases must *not* be cdef classes.)
* Type inference is now supported for Pythran compiled NumPy expressions.
Patch by Nils Braun. (Github issue 1954)
* The ``const`` modifier can be applied to memoryview declarations to allow
read-only buffers as input. (Github issues 1605, 1869)
* C code in the docstring of a ``cdef extern`` block is copied verbatimly
into the generated file.
Patch by Jeroen Demeyer. (Github issue 1915)
* When compiling with gcc, the module init function is now tuned for small
code size instead of whatever compile flags were provided externally.
Cython now also disables some code intensive optimisations in that function
to further reduce the code size. (Github issue 2102)
* Decorating an async coroutine with ``cython.iterable_coroutine`` changes its
type at compile time to make it iterable. While this is not strictly in line
with PEP-492, it improves the interoperability with old-style coroutines that
use ``yield from`` instead of ``await``.
* The IPython magic has preliminary support for JupyterLab.
(Github issue 1775)
* The new TSS C-API in CPython 3.7 is supported and has been backported.
Patch by Naotoshi Seo. (Github issue 1932)
* Cython knows the new ``Py_tss_t`` type defined in PEP-539 and automatically
initialises variables declared with that type to ``Py_tss_NEEDS_INIT``,
a value which cannot be used outside of static assignments.
* The set methods ``.remove()`` and ``.discard()`` are optimised.
Patch by Antoine Pitrou. (Github issue 2042)
* ``dict.pop()`` is optimised.
Original patch by Antoine Pitrou. (Github issue 2047)
* Iteration over sets and frozensets is optimised.
(Github issue 2048)
* Safe integer loops (< range(2^30)) are automatically optimised into C loops.
* ``alist.extend([a,b,c])`` is optimised into sequential ``list.append()`` calls
for short literal sequences.
* Calls to builtin methods that are not specifically optimised into C-API calls
now use a cache that avoids repeated lookups of the underlying C function.
(Github issue 2054)
* Single argument function calls can avoid the argument tuple creation in some cases.
* Some redundant extension type checks are avoided.
* Formatting C enum values in f-strings is faster, as well as some other special cases.
* String formatting with the '%' operator is optimised into f-strings in simple cases.
* Subscripting (item access) is faster in some cases.
* Some ``bytearray`` operations have been optimised similar to ``bytes``.
* Some PEP-484/526 container type declarations are now considered for
loop optimisations.
* Indexing into memoryview slices with ``view[i][j]`` is now optimised into
``view[i, j]``.
* Python compatible ``cython.*`` types can now be mixed with type declarations
in Cython syntax.
* Name lookups in the module and in classes are faster.
* Python attribute lookups on extension types without instance dict are faster.
* Some missing signals were added to ``libc/signal.pxd``.
Patch by Jeroen Demeyer. (Github issue 1914)
* The warning about repeated extern declarations is now visible by default.
(Github issue 1874)
* The exception handling of the function types used by CPython's type slot
functions was corrected to match the de-facto standard behaviour, so that
code that uses them directly benefits from automatic and correct exception
propagation. Patch by Jeroen Demeyer. (Github issue 1980)
* Defining the macro ``CYTHON_NO_PYINIT_EXPORT`` will prevent the module init
function from being exported as symbol, e.g. when linking modules statically
in an embedding setup. Patch by AraHaan. (Github issue 1944)
Bugs fixed
----------
* If a module name is explicitly provided for an ``Extension()`` that is compiled
via ``cythonize()``, it was previously ignored and replaced by the source file
name. It can now be used to override the target module name, e.g. for compiling
prefixed accelerator modules from Python files. (Github issue 2038)
* The arguments of the ``num_threads`` parameter of parallel sections
were not sufficiently validated and could lead to invalid C code.
(Github issue 1957)
* Catching exceptions with a non-trivial exception pattern could call into
CPython with a live exception set. This triggered incorrect behaviour
and crashes, especially in CPython 3.7.
* The signature of the special ``__richcmp__()`` method was corrected to recognise
the type of the first argument as ``self``. It was previously treated as plain
object, but CPython actually guarantees that it always has the correct type.
Note: this can change the semantics of user code that previously relied on
``self`` being untyped.
* Some Python 3 exceptions were not recognised as builtins when running Cython
under Python 2.
* Some async helper functions were not defined in the generated C code when
compiling simple async code. (Github issue 2075)
* Line tracing did not include generators and coroutines.
(Github issue 1949)
* C++ declarations for ``unordered_map`` were corrected.
Patch by Michael Schatzow. (Github issue 1484)
* Iterator declarations in C++ ``deque`` and ``vector`` were corrected.
Patch by Alex Huszagh. (Github issue 1870)
* The const modifiers in the C++ ``string`` declarations were corrected, together
with the coercion behaviour of string literals into C++ strings.
(Github issue 2132)
* Some declaration types in ``libc.limits`` were corrected.
Patch by Jeroen Demeyer. (Github issue 2016)
* ``cython.final`` was not accepted on Python classes with an ``cython.cclass``
decorator. (Github issue 2040)
* Cython no longer creates useless and incorrect ``PyInstanceMethod`` wrappers for
methods in Python 3. Patch by Jeroen Demeyer. (Github issue 2105)
* The builtin ``bytearray`` type could not be used as base type of cdef classes.
(Github issue 2106)
Other changes
-------------