Closes #1603.

… and enforce them with pycodestyle.

Fixes https://github.com/cython/cython/issues/3642

Fixes https://github.com/cython/cython/issues/3642

This avoids the METH_O function signature by default, since it does not match normal Python semantics.

* Fix unicode name handling of no-args functions when allowing keywords.

* Fix a crash when a keyword argument is passed to a function that does not allow them. Previously, the reported key name was not set and thus NULL.

* Extend "always_allow_keywords" test to cover some edge cases.
Some are commented out as they currently only work with the fastcall implementation.

Use an inlined version of PyType_HasFeature() instead of directly accessing "tp_flags" in the generated code.

Avoid an additional utility code section for 2-exception matching by relying on existing special-cased macros.

Avoid generating an "abort()" check for known non-0 steps in prange(). Instead, make it a compile time error if we know it's zero.

Add comment to explain why "better" GIL handling is not needed in special methods (because it's held anyway).

Closes https://github.com/cython/cython/issues/3590

Fix a C compiler warning about unused cleanup code in buffer using functions that always raise (found by clang in the bufaccess.pyx test).

* Rewrite C property support (GH-2640) based on inline C methods.
Supersedes GH-2640 and GH-3095.
Closes GH-3521.

* Test fix for `numpy_parallel.pyx`: avoid depending on whether "nd.shape" requires the GIL or not.

* Turn NumPy's "ndarray.data" into a property to avoid direct struct access.

* Make "ndarray.size" accessible without the GIL.

Prevent VerboseCodeWriter from inserting nul-bytes into the C file by switching to a more "standard" way of inserting code at a later time.

Fix duplicate code generation in assert condition, found for lambda functions that are used as conditions in "test_grammar.py".

This allows taking advantage of the automatic "with gil" block handling for raising exceptions, allows proper control flow analysis, etc.

Always call the refnanny on function exit if we set it up on entry, not just in GIL-owning functions.
This was previously using inconsistent conditions on entry and exit of the function.

Instead of simply asserting that the error exit case and the success exit case of a nogil function are aligned, make sure they are before joining them back together.
This is necessary because the error code path is more likely to require the GIL for cleanup operations than the success path – which is a good thing, actually, so we try to streamline the success case at the expense of more work on the error path.

Move assertion where it actually belongs, since it does not apply to the buffer cleanup case (which semantically jumps over it with a 'goto').

Move the branch-hint generation from Nodes.py into Optimize.py to make it available to tree assertion tests (and add such a test).

Support the 'assert' statement in nogil sections, as long as it has a plain C condition and constant message (string) value.

Closes #3558.

Acquire the GIL in nogil functions only when strictly needed on function exit, e.g. for cleaning up temp variables from with-gil blocks or adding tracebacks.

Closes GH-3554.

Follows Python behaviour, but excludes "__pyx_…" names in utility code.

Closes GH-1382.

Right now it's used in a few simple cases (function call and single assignment)
Don't attempt to remove reference types.
Be wary of the "safety check" for double moves when things like result() are called twice
Made sure fallback option was genuinely c++03 complient so that test should pass on clang

Closes #2753.

Add __Pyx_IS_TYPE() macro to mimic the new "Py_IS_TYPE()" macro in CPython 3.9 that replaces the "Py_TYPE() == …" type check pattern.

Fix branch prediction hints for plain (unlikely/exceptional) "raise" statements in if/else clauses that are not preceded by other statements.

These were previously getting missed. Added code to specialize them and tests to prove it.

Fixes https://github.com/cython/cython/issues/3142

Also fixes https://github.com/cython/cython/issues/3460 - (seems related enough to go in the same PR)