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# Code adapted from:
#
# http://code.activestate.com/recipes/204197-solving-the-metaclass-conflict/
#
# The code at the above URL was released under the PSF license.
import inspect
import types
from glue.external import six
if six.PY2:
import __builtin__
CLASS_TYPE = types.ClassType
else:
import builtins
CLASS_TYPE = type
__all__ = ['classmaker']
def skip_redundant(iterable, skipset=None):
"""
Redundant items are repeated items or items in the original skipset.
"""
if skipset is None:
skipset = set()
for item in iterable:
if item not in skipset:
skipset.add(item)
yield item
def remove_redundant(metaclasses):
skipset = set([CLASS_TYPE])
for meta in metaclasses: # determines the metaclasses to be skipped
skipset.update(inspect.getmro(meta)[1:])
return tuple(skip_redundant(metaclasses, skipset))
memoized_metaclasses_map = {}
def get_noconflict_metaclass(bases, left_metas, right_metas):
"""
Not intended to be used outside of this module, unless you know
what you are doing.
"""
# make tuple of needed metaclasses in specified priority order
metas = left_metas + tuple(map(type, bases)) + right_metas
needed_metas = remove_redundant(metas)
# return existing confict-solving meta, if any
if needed_metas in memoized_metaclasses_map:
return memoized_metaclasses_map[needed_metas]
# nope: compute, memoize and return needed conflict-solving meta
elif not needed_metas: # wee, a trivial case, happy us
meta = type
elif len(needed_metas) == 1: # another trivial case
meta = needed_metas[0]
# check for recursion, can happen i.e. for Zope ExtensionClasses
elif needed_metas == bases:
raise TypeError("Incompatible root metatypes", needed_metas)
else: # gotta work ...
metaname = '_' + ''.join([m.__name__ for m in needed_metas])
meta = classmaker()(metaname, needed_metas, {})
memoized_metaclasses_map[needed_metas] = meta
return meta
def classmaker(left_metas=(), right_metas=()):
def make_class(name, bases, adict):
metaclass = get_noconflict_metaclass(
bases, left_metas, right_metas)
return metaclass(name, bases, adict)
return make_class
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