[Zope3-checkins] CVS: Zope3/src/zope/interface - advice.py:1.1 declarations.py:1.13

Phillip J. Eby pje@telecommunity.com
Tue, 3 Jun 2003 15:53:10 -0400


Update of /cvs-repository/Zope3/src/zope/interface
In directory cvs.zope.org:/tmp/cvs-serv13891

Modified Files:
	declarations.py 
Added Files:
	advice.py 
Log Message:
Checking in Steve Alexander's versions of my contributed code to support
"magic metaclass" declarations.  I'm checking this in solely to make my 
contribution of the code official.  I have not attempted to verify Steve's
changes to Zope or that his changes haven't broken anything in the 
contributed code.  I'm assuming that Steve has already verified this code 
in his private workspace.


=== Added File Zope3/src/zope/interface/advice.py ===
##############################################################################
#
# Copyright (c) 2003 Zope Corporation and Contributors.
# All Rights Reserved.
#
# This software is subject to the provisions of the Zope Public License,
# Version 2.0 (ZPL).  A copy of the ZPL should accompany this distribution.
# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
# FOR A PARTICULAR PURPOSE.
#
##############################################################################
"""Class advice.

This module was adapted from 'protocols.advice', part of the Python
Enterprise Application Kit (PEAK).  Please notify the PEAK authors
(pje@telecommunity.com and tsarna@sarna.org) if bugs are found or
Zope-specific changes are required, so that the PEAK version of this module
can be kept in sync.

PEAK is a Python application framework that interoperates with (but does
not require) Zope 3 and Twisted.  It provides tools for manipulating UML
models, object-relational persistence, aspect-oriented programming, and more.
Visit the PEAK home page at http://peak.telecommunity.com for more information.

$Id: advice.py,v 1.1 2003/06/03 19:52:39 pje Exp $
"""

from types import ClassType, FunctionType
import sys

def getFrameInfo(frame):
    """Return (kind,module,locals,globals) for a frame

    'kind' is one of "exec", "module", "class", "function call", or "unknown".
    """

    f_locals = frame.f_locals
    f_globals = frame.f_globals

    sameNamespace = f_locals is f_globals
    hasModule = '__module__' in f_locals
    hasName = '__name__' in f_globals

    sameName = hasModule and hasName
    sameName = sameName and f_globals['__name__']==f_locals['__module__']

    module = hasName and sys.modules.get(f_globals['__name__']) or None

    namespaceIsModule = module and module.__dict__ is f_globals

    if not namespaceIsModule:
        # some kind of funky exec
        kind = "exec"
    elif sameNamespace and not hasModule:
        kind = "module"
    elif sameName and not sameNamespace:
        kind = "class"
    elif not sameNamespace:
        kind = "function call"
    else:
        # How can you have f_locals is f_globals, and have '__module__' set?
        # This is probably module-level code, but with a '__module__' variable.
        kind = "unknown"
    return kind, module, f_locals, f_globals


def addClassAdvisor(callback, depth=2):
    """Set up 'callback' to be passed the containing class upon creation

    This function is designed to be called by an "advising" function executed
    in a class suite.  The "advising" function supplies a callback that it
    wishes to have executed when the containing class is created.  The
    callback will be given one argument: the newly created containing class.
    The return value of the callback will be used in place of the class, so
    the callback should return the input if it does not wish to replace the
    class.

    The optional 'depth' argument to this function determines the number of
    frames between this function and the targeted class suite.  'depth'
    defaults to 2, since this skips this function's frame and one calling
    function frame.  If you use this function from a function called directly
    in the class suite, the default will be correct, otherwise you will need
    to determine the correct depth yourself.

    This function works by installing a special class factory function in
    place of the '__metaclass__' of the containing class.  Therefore, only
    callbacks *after* the last '__metaclass__' assignment in the containing
    class will be executed.  Be sure that classes using "advising" functions
    declare any '__metaclass__' *first*, to ensure all callbacks are run."""

    frame = sys._getframe(depth)
    kind, module, caller_locals, caller_globals = getFrameInfo(frame)

    # This causes a problem when zope interfaces are used from doctest.
    # In these cases, kind == "exec".
    #
    #if kind != "class":
    #    raise SyntaxError(
    #        "Advice must be in the body of a class statement"
    #    )

    previousMetaclass = caller_locals.get('__metaclass__')
    defaultMetaclass  = caller_globals.get('__metaclass__', ClassType)


    def advise(name, bases, cdict):

        if '__metaclass__' in cdict:
            del cdict['__metaclass__']

        if previousMetaclass is None:
             if bases:
                 # find best metaclass or use global __metaclass__ if no bases
                 meta = determineMetaclass(bases)
             else:
                 meta = defaultMetaclass

        elif isClassAdvisor(previousMetaclass):
            # special case: we can't compute the "true" metaclass here,
            # so we need to invoke the previous metaclass and let it
            # figure it out for us (and apply its own advice in the process)
            meta = previousMetaclass

        else:
            meta = determineMetaclass(bases, previousMetaclass)

        newClass = meta(name,bases,cdict)

        # this lets the callback replace the class completely, if it wants to
        return callback(newClass)

    # introspection data only, not used by inner function
    advise.previousMetaclass = previousMetaclass
    advise.callback = callback

    # install the advisor
    caller_locals['__metaclass__'] = advise


def isClassAdvisor(ob):
    """True if 'ob' is a class advisor function"""
    return isinstance(ob,FunctionType) and hasattr(ob,'previousMetaclass')


def determineMetaclass(bases, explicit_mc=None):
    """Determine metaclass from 1+ bases and optional explicit __metaclass__"""

    meta = [getattr(b,'__class__',type(b)) for b in bases]

    if explicit_mc is not None:
        # The explicit metaclass needs to be verified for compatibility
        # as well, and allowed to resolve the incompatible bases, if any
        meta.append(explicit_mc)

    if len(meta)==1:
        # easy case
        return meta[0]

    candidates = minimalBases(meta) # minimal set of metaclasses

    if not candidates:
        # they're all "classic" classes
        return ClassType

    elif len(candidates)>1:
        # We could auto-combine, but for now we won't...
        raise TypeError("Incompatible metatypes",bases)

    # Just one, return it
    return candidates[0]


def minimalBases(classes):
    """Reduce a list of base classes to its ordered minimum equivalent"""

    classes = [c for c in classes if c is not ClassType]
    candidates = []

    for m in classes:
        for n in classes:
            if issubclass(n,m) and m is not n:
                break
        else:
            # m has no subclasses in 'classes'
            if m in candidates:
                candidates.remove(m)    # ensure that we're later in the list
            candidates.append(m)

    return candidates



=== Zope3/src/zope/interface/declarations.py 1.12 => 1.13 ===
--- Zope3/src/zope/interface/declarations.py:1.12	Mon Jun  2 10:46:15 2003
+++ Zope3/src/zope/interface/declarations.py	Tue Jun  3 15:52:39 2003
@@ -18,6 +18,7 @@
 from zope.interface.interface import InterfaceClass, mergeOrderings
 import exceptions
 from types import ClassType
+from advice import addClassAdvisor
 
 # There are imports from _zope_interface_ospec later in the file
 # because _zope_interface_ospec depends on some functions defined
@@ -358,10 +359,10 @@
         if provides is not None:
             # Just use the provides spec
             return provides
-        
+
         # No interfaces
         return _empty
-        
+
     return ObjectSpecification(provides, cls)
 
 def providedBy(ob):
@@ -979,24 +980,9 @@
     """
     return getattr(object, "__provides__", _empty)
 
-
-class metaclasshooker:
-
-    def __init__(self, metaclass):
-        self.metaclass = metaclass
-
-    def __call__(self, name, bases, dict):
-        metaclass = self.metaclass
-        if metaclass is None:
-            if bases:
-                metaclass = type(bases[0])
-            else:
-                metaclass = ClassType
-
-        cls = metaclass(name, bases, dict)
-        _setImplements(cls, dict['__implements__'])
-
-        return cls
+def _implements_advice(cls):
+    _setImplements(cls, cls.__dict__['__implements__'])
+    return cls
 
 def _implements(name, spec):
     frame = sys._getframe(2)
@@ -1010,11 +996,7 @@
         raise TypeError(name+" can be used only once in a class definition.")
 
     locals["__implements__"] = spec
-
-    metaclass = locals.get('__metaclass__')
-    if metaclass is None:
-        metaclass = frame.f_globals.get('__metaclass__')
-    locals["__metaclass__"] = metaclasshooker(metaclass)
+    addClassAdvisor(_implements_advice, depth=3)
 
 def implements(*interfaces):
     """Declare interfaces implemented by instances of a class
@@ -1295,7 +1277,7 @@
 def _finddescr(cls):
     # Try to find the __providedBy__ descriptor. If we can't find it,
     # just return the class. 
-    
+
     d = cls.__dict__.get("__providedBy__", cls)
     if d is not cls:
         return d
@@ -1337,7 +1319,7 @@
                         break
                 else: # no break
                     pb = None
-                    
+
             if not isinstance(pb, ObjectSpecificationDescriptor):
                 raise TypeError(
                     cls,