| 1 | """Generic metaclass.
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| 2 |
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| 3 | XXX This is very much a work in progress.
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| 4 |
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| 5 | """
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| 6 |
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| 7 | import types
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| 8 |
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| 9 | class MetaMethodWrapper:
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| 10 |
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| 11 | def __init__(self, func, inst):
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| 12 | self.func = func
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| 13 | self.inst = inst
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| 14 | self.__name__ = self.func.__name__
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| 15 |
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| 16 | def __call__(self, *args, **kw):
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| 17 | return apply(self.func, (self.inst,) + args, kw)
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| 18 |
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| 19 | class MetaHelper:
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| 20 |
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| 21 | __methodwrapper__ = MetaMethodWrapper # For derived helpers to override
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| 22 |
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| 23 | def __helperinit__(self, formalclass):
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| 24 | self.__formalclass__ = formalclass
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| 25 |
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| 26 | def __getattr__(self, name):
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| 27 | # Invoked for any attr not in the instance's __dict__
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| 28 | try:
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| 29 | raw = self.__formalclass__.__getattr__(name)
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| 30 | except AttributeError:
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| 31 | try:
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| 32 | ga = self.__formalclass__.__getattr__('__usergetattr__')
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| 33 | except (KeyError, AttributeError):
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| 34 | raise AttributeError, name
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| 35 | return ga(self, name)
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| 36 | if type(raw) != types.FunctionType:
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| 37 | return raw
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| 38 | return self.__methodwrapper__(raw, self)
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| 39 |
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| 40 | class MetaClass:
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| 41 |
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| 42 | """A generic metaclass.
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| 43 |
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| 44 | This can be subclassed to implement various kinds of meta-behavior.
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| 45 |
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| 46 | """
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| 47 |
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| 48 | __helper__ = MetaHelper # For derived metaclasses to override
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| 49 |
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| 50 | __inited = 0
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| 51 |
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| 52 | def __init__(self, name, bases, dict):
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| 53 | try:
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| 54 | ga = dict['__getattr__']
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| 55 | except KeyError:
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| 56 | pass
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| 57 | else:
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| 58 | dict['__usergetattr__'] = ga
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| 59 | del dict['__getattr__']
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| 60 | self.__name__ = name
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| 61 | self.__bases__ = bases
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| 62 | self.__realdict__ = dict
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| 63 | self.__inited = 1
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| 64 |
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| 65 | def __getattr__(self, name):
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| 66 | try:
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| 67 | return self.__realdict__[name]
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| 68 | except KeyError:
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| 69 | for base in self.__bases__:
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| 70 | try:
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| 71 | return base.__getattr__(name)
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| 72 | except AttributeError:
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| 73 | pass
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| 74 | raise AttributeError, name
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| 75 |
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| 76 | def __setattr__(self, name, value):
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| 77 | if not self.__inited:
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| 78 | self.__dict__[name] = value
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| 79 | else:
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| 80 | self.__realdict__[name] = value
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| 81 |
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| 82 | def __call__(self, *args, **kw):
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| 83 | inst = self.__helper__()
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| 84 | inst.__helperinit__(self)
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| 85 | try:
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| 86 | init = inst.__getattr__('__init__')
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| 87 | except AttributeError:
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| 88 | init = lambda: None
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| 89 | apply(init, args, kw)
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| 90 | return inst
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| 91 |
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| 92 |
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| 93 | Meta = MetaClass('Meta', (), {})
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| 94 |
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| 95 |
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| 96 | def _test():
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| 97 | class C(Meta):
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| 98 | def __init__(self, *args):
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| 99 | print "__init__, args =", args
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| 100 | def m1(self, x):
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| 101 | print "m1(x=%r)" % (x,)
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| 102 | print C
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| 103 | x = C()
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| 104 | print x
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| 105 | x.m1(12)
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| 106 | class D(C):
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| 107 | def __getattr__(self, name):
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| 108 | if name[:2] == '__': raise AttributeError, name
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| 109 | return "getattr:%s" % name
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| 110 | x = D()
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| 111 | print x.foo
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| 112 | print x._foo
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| 113 | ## print x.__foo
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| 114 | ## print x.__foo__
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| 115 |
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| 116 |
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| 117 | if __name__ == '__main__':
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| 118 | _test()
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