Arbitrary point checkpoint commit. Take no notice.

Demo/metaclasses/Meta.py

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+"""Generic metaclass.
+
+XXX This is very much a work in progress.
+
+"""
+
+import types
+
+class MetaMethodWrapper:
+
+    def __init__(self, func, inst):
+	self.func = func
+	self.inst = inst
+	self.__name__ = self.func.__name__
+
+    def __call__(self, *args, **kw):
+	return apply(self.func, (self.inst,) + args, kw)
+
+class MetaHelper:
+
+    __methodwrapper__ = MetaMethodWrapper # For derived helpers to override
+
+    def __helperinit__(self, formalclass):
+	self.__formalclass__ = formalclass
+
+    def __getattr__(self, name):
+	# Invoked for any attr not in the instance's __dict__
+	try:
+	    raw = self.__formalclass__.__getattr__(name)
+	except AttributeError:
+	    try:
+		_getattr_ = self.__dict__['_getattr_']
+	    except KeyError:
+		raise AttributeError, name
+	    return _getattr_(name)
+	if type(raw) != types.FunctionType:
+	    return raw
+	return self.__methodwrapper__(raw, self)
+
+class MetaClass:
+
+    """A generic metaclass.
+
+    This can be subclassed to implement various kinds of meta-behavior.
+
+    """
+
+    __helper__ = MetaHelper		# For derived metaclasses to override
+
+    __inited = 0
+
+    def __init__(self, name, bases, dict):
+	if dict.has_key('__getattr__'):
+	    raise TypeError, "Can't override __getattr__; use _getattr_"
+	self.__name__ = name
+	self.__bases__ = bases
+	self.__realdict__ = dict
+	self.__inited = 1
+
+    def __getattr__(self, name):
+	try:
+	    return self.__realdict__[name]
+	except KeyError:
+	    for base in self.__bases__:
+		try:
+		    return base.__getattr__(name)
+		except AttributeError:
+		    pass
+	    raise AttributeError, name
+
+    def __setattr__(self, name, value):
+	if not self.__inited:
+	    self.__dict__[name] = value
+	else:
+	    self.__realdict__[name] = value
+
+    def __call__(self, *args, **kw):
+	inst = self.__helper__()
+	inst.__helperinit__(self)
+	try:
+	    init = inst.__getattr__('__init__')
+	except AttributeError:
+	    init = lambda: None
+	apply(init, args, kw)
+	return inst
+    
+
+Meta = MetaClass('Meta', (), {})
+
+
+def _test():
+    class C(Meta):
+	def __init__(self, *args):
+	    print "__init__, args =", args
+	def m1(self, x):
+	    print "m1(x=%s)" %`x`
+    print C
+    x = C()
+    print x
+    x.m1(12)
+    
+
+if __name__ == '__main__':
+    _test()
+
+