On 12/04/18 17:12, Jeroen Demeyer wrote:
Dear Python developers,
I would like to request a review of PEP 575, which is about changing the
classes used for built-in functions and Python functions and methods.
The text of the PEP can be found at
The motivation of PEP 575 is to allow introspection of built-in
functions and to allow functions implemented in Python to be
re-implemented in C.
These are excellent goals.
The PEP then elaborates a complex class hierarchy, and various
extensions to the C API.
This adds a considerable maintainance burden and restricts future
changes and optimisations to CPython.
While a unified *interface* makes sense, a unified class hierarchy and
implementation, IMO, do not.
The hierarchy also seems to force classes that are dissimilar to share a
common base-class.
Bound-methods may be callables, but they are not functions, they are a
pair of a function and a "self" object.
As the PEP points out, Cython functions are able to mimic Python
functions, why not do the same for CPython builtin-functions?
As an aside, rather than unifying the classes of all non-class
callables, CPython's builtin-function class could be split in two.
Currently it is both a bound-method and a function.
The name 'builtin_function_or_method' is a give away :)
Consider the most common "function" and "method" classes:
>>> class C:
... def f(self): pass
# "functions"
>>> type(C.f)
<class 'function'>
>>> type(len)
<class 'builtin_function_or_method'>
>>> type(list.append)
<class 'method_descriptor'>
>>> type(int.__add__)
<class 'wrapper_descriptor'>
# "bound-methods"
>>> type(C().f)
<class 'method'>
>>> type([].append)
<class 'builtin_function_or_method'>
>>> type(1 .__add__)
<class 'method-wrapper'>
IMO, there are so many versions of "function" and "bound-method", that a
unified class hierarchy and the resulting restriction to the
implementation will make implementing a unified interface harder, not
easier.
For "functions", all that is needed is to specify an interface, say a
single property "__signature__".
Then all that a class that wants to be a "function" need do is have a
"__signature__" property and be callable.
For "bound-methods", we should reuse the interface of 'method';
two properties, "__func__" and "__self__".
Cheers,
Mark.
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