[WIP] Introduce signature utilities for python 3.8

[4383]

To prevent stdlib getfullargspec deprecation these propose to introduce
a backward compat for python version who will remove getfullargspec.

These changes are more to discuss with you about the cross vendoring between mako, dogpile etc...

related to #154

[zzzeek]

OK so my notion was, since this has to be in four projects, to lift the Python 3.3 version, which apparently is not on github, so it's this:

FullArgSpec = namedtuple('FullArgSpec',
    'args, varargs, varkw, defaults, kwonlyargs, kwonlydefaults, annotations')

def getfullargspec(func):
    """Get the names and default values of a function's arguments.

    A tuple of seven things is returned:
    (args, varargs, varkw, defaults, kwonlyargs, kwonlydefaults annotations).
    'args' is a list of the argument names.
    'varargs' and 'varkw' are the names of the * and ** arguments or None.
    'defaults' is an n-tuple of the default values of the last n arguments.
    'kwonlyargs' is a list of keyword-only argument names.
    'kwonlydefaults' is a dictionary mapping names from kwonlyargs to defaults.
    'annotations' is a dictionary mapping argument names to annotations.

    The first four items in the tuple correspond to getargspec().
    """

    if ismethod(func):
        func = func.__func__
    if not isfunction(func):
        raise TypeError('{!r} is not a Python function'.format(func))
    args, varargs, kwonlyargs, varkw = _getfullargs(func.__code__)
    return FullArgSpec(args, varargs, varkw, func.__defaults__,
            kwonlyargs, func.__kwdefaults__, func.__annotations__)

def _getfullargs(co):
    """Get information about the arguments accepted by a code object.

    Four things are returned: (args, varargs, kwonlyargs, varkw), where
    'args' and 'kwonlyargs' are lists of argument names, and 'varargs'
    and 'varkw' are the names of the * and ** arguments or None."""

    if not iscode(co):
        raise TypeError('{!r} is not a code object'.format(co))

    nargs = co.co_argcount
    names = co.co_varnames
    nkwargs = co.co_kwonlyargcount
    args = list(names[:nargs])
    kwonlyargs = list(names[nargs:nargs+nkwargs])
    step = 0

    nargs += nkwargs
    varargs = None
    if co.co_flags & CO_VARARGS:
        varargs = co.co_varnames[nargs]
        nargs = nargs + 1
    varkw = None
    if co.co_flags & CO_VARKEYWORDS:
        varkw = co.co_varnames[nargs]
    return args, varargs, kwonlyargs, varkw

per my performance test at https://gist.github.com/zzzeek/0eb0636fa3917f36ffd887d9f765c208 it is 5-20x faster than any current implementation

[4383]

I've intialize this project based on the py3.3 code => https://github.com/4383/contrat
Quick and dirty if you want to take a look.

(I use pbr to package it but I can also use vanilla setuptools/distutils)

[zzzeek]

sorry I know im being difficult here, I was looking for to make a very truncated version just of getfullargspec() and then have it present directly in each project (dogpile, mako, alembic, sqlalchemy). I don't want to make an additional package because 1. external dependency 2. competes with upstream Python who will want to be fixing Signature's performance 3. not sure if the 3.3 implementation is even going to work b.c. i need to see what syntaxes we might be missing .

if you want I can annotate everything at https://github.com/4383/contrat/blob/master/contrat/__init__.py that I don't need

[zzzeek]

also note they are un-deprecating getfullargspec() for now. so we have time. I do want to improve on performance thoguh but tihs is more important for sqlalchemy

[4383]

sorry I know im being difficult here,

No problem

I was looking for to make a very truncated version just of getfullargspec() and then have it present directly in each project (dogpile, mako, alembic, sqlalchemy). I don't want to make an additional package because 1. external dependency 2. competes with upstream Python who will want to be fixing Signature's performance 3. not sure if the 3.3 implementation is even going to work b.c. i need to see what syntaxes we might be missing .

if you want I can annotate everything at https://github.com/4383/contrat/blob/master/contrat/__init__.py that I don't need

Yeah good idea

[4383]

also note they are un-deprecating getfullargspec() for now. so we have time. I do want to improve on performance thoguh but tihs is more important for sqlalchemy

Yep I know

[4383]

I guess I can close this one now (related to d0ff02b)

[zzzeek]

yeah I did them all at once!