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PEP 670: formatting #2117

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Oct 19, 2021
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PEP 670: formatting #2117

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28 changes: 15 additions & 13 deletions pep-0670.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,8 @@ Abstract
Convert macros to static inline functions or regular functions.

Remove the return value of macros having a return value, whereas they
should not, to detect bugs in C extensions when the C API is misused.
should not, to aid detecting bugs in C extensions when the C API is
misused.

Some function arguments are still cast to ``PyObject*`` to prevent
emitting new compiler warnings.
Expand All @@ -25,8 +26,8 @@ Rationale
=========

The use of macros may have unintended adverse effects that are hard to
avoid, even for experienced C developers. Some issues have been known for
years, while others have been discovered recently in Python.
avoid, even for experienced C developers. Some issues have been known
for years, while others have been discovered recently in Python.
Working around macro pitfalls makes the macro coder harder to read and
to maintain.

Expand Down Expand Up @@ -67,9 +68,9 @@ common macro pitfalls:
Performance and inlining
========================

Static inline functions is a feature added to the C99 standard. Modern
C compilers have efficient heuristics to decide if a function should be inlined
or not.
Static inline functions is a feature added to the C99 standard. Modern C
compilers have efficient heuristics to decide if a function should be
inlined or not.

When a C compiler decides to not inline, there is likely a good reason.
For example, inlining would reuse a register which require to
Expand All @@ -90,8 +91,8 @@ decide if function should be inlined or not.
Force inlining
--------------

The ``Py_ALWAYS_INLINE`` macro can be used to force inlining. This macro uses
``__attribute__((always_inline))`` with GCC and Clang, and
The ``Py_ALWAYS_INLINE`` macro can be used to force inlining. This macro
uses ``__attribute__((always_inline))`` with GCC and Clang, and
``__forceinline`` with MSC.

So far, previous attempts to use ``Py_ALWAYS_INLINE`` didn't show any
Expand Down Expand Up @@ -163,7 +164,8 @@ functions.

The performance impact of such conversion should be measured with
benchmarks. If there is a significant slowdown, there should be a good
reason to do the conversion. One reason can be hiding implementation details.
reason to do the conversion. One reason can be hiding implementation
details.

Using static inline functions in the internal C API is fine: the
internal C API exposes implemenation details by design and should not be
Expand Down Expand Up @@ -191,8 +193,8 @@ For example, the ``Py_TYPE(obj)`` macro casts its ``obj`` argument to
The undocumented private ``_Py_TYPE()`` function must not be called
directly. Only the documented public ``Py_TYPE()`` macro must be used.

Later, the cast can be removed on a case by case basis, but that is out of
scope for this PEP.
Later, the cast can be removed on a case by case basis, but that is out
of scope for this PEP.

Remove the return value
-----------------------
Expand All @@ -205,8 +207,8 @@ misused in third party C extensions. See `bpo-30459
notice this issue while reviewing macro code.

These macros are converted to functions using the ``void`` return type
to remove their return value. Removing the return value aids detecting bugs in
C extensions when the C API is misused.
to remove their return value. Removing the return value aids detecting
bugs in C extensions when the C API is misused.


Backwards Compatibility
Expand Down