| 1 | """Tracing 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, sys
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| 8 |
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| 9 | class TraceMetaClass:
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| 10 | """Metaclass for tracing.
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| 11 |
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| 12 | Classes defined using this metaclass have an automatic tracing
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| 13 | feature -- by setting the __trace_output__ instance (or class)
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| 14 | variable to a file object, trace messages about all calls are
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| 15 | written to the file. The trace formatting can be changed by
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| 16 | defining a suitable __trace_call__ method.
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| 17 |
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| 18 | """
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| 19 |
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| 20 | __inited = 0
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| 21 |
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| 22 | def __init__(self, name, bases, dict):
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| 23 | self.__name__ = name
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| 24 | self.__bases__ = bases
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| 25 | self.__dict = dict
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| 26 | # XXX Can't define __dict__, alas
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| 27 | self.__inited = 1
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| 28 |
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| 29 | def __getattr__(self, name):
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| 30 | try:
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| 31 | return self.__dict[name]
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| 32 | except KeyError:
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| 33 | for base in self.__bases__:
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| 34 | try:
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| 35 | return base.__getattr__(name)
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| 36 | except AttributeError:
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| 37 | pass
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| 38 | raise AttributeError, name
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| 39 |
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| 40 | def __setattr__(self, name, value):
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| 41 | if not self.__inited:
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| 42 | self.__dict__[name] = value
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| 43 | else:
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| 44 | self.__dict[name] = value
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| 45 |
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| 46 | def __call__(self, *args, **kw):
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| 47 | inst = TracingInstance()
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| 48 | inst.__meta_init__(self)
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| 49 | try:
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| 50 | init = inst.__getattr__('__init__')
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| 51 | except AttributeError:
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| 52 | init = lambda: None
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| 53 | apply(init, args, kw)
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| 54 | return inst
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| 55 |
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| 56 | __trace_output__ = None
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| 57 |
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| 58 | class TracingInstance:
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| 59 | """Helper class to represent an instance of a tracing class."""
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| 60 |
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| 61 | def __trace_call__(self, fp, fmt, *args):
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| 62 | fp.write((fmt+'\n') % args)
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| 63 |
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| 64 | def __meta_init__(self, klass):
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| 65 | self.__class = klass
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| 66 |
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| 67 | def __getattr__(self, name):
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| 68 | # Invoked for any attr not in the instance's __dict__
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| 69 | try:
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| 70 | raw = self.__class.__getattr__(name)
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| 71 | except AttributeError:
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| 72 | raise AttributeError, name
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| 73 | if type(raw) != types.FunctionType:
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| 74 | return raw
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| 75 | # It's a function
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| 76 | fullname = self.__class.__name__ + "." + name
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| 77 | if not self.__trace_output__ or name == '__trace_call__':
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| 78 | return NotTracingWrapper(fullname, raw, self)
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| 79 | else:
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| 80 | return TracingWrapper(fullname, raw, self)
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| 81 |
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| 82 | class NotTracingWrapper:
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| 83 | def __init__(self, name, func, inst):
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| 84 | self.__name__ = name
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| 85 | self.func = func
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| 86 | self.inst = inst
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| 87 | def __call__(self, *args, **kw):
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| 88 | return apply(self.func, (self.inst,) + args, kw)
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| 89 |
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| 90 | class TracingWrapper(NotTracingWrapper):
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| 91 | def __call__(self, *args, **kw):
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| 92 | self.inst.__trace_call__(self.inst.__trace_output__,
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| 93 | "calling %s, inst=%s, args=%s, kw=%s",
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| 94 | self.__name__, self.inst, args, kw)
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| 95 | try:
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| 96 | rv = apply(self.func, (self.inst,) + args, kw)
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| 97 | except:
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| 98 | t, v, tb = sys.exc_info()
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| 99 | self.inst.__trace_call__(self.inst.__trace_output__,
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| 100 | "returning from %s with exception %s: %s",
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| 101 | self.__name__, t, v)
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| 102 | raise t, v, tb
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| 103 | else:
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| 104 | self.inst.__trace_call__(self.inst.__trace_output__,
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| 105 | "returning from %s with value %s",
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| 106 | self.__name__, rv)
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| 107 | return rv
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| 108 |
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| 109 | Traced = TraceMetaClass('Traced', (), {'__trace_output__': None})
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| 110 |
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| 111 |
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| 112 | def _test():
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| 113 | global C, D
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| 114 | class C(Traced):
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| 115 | def __init__(self, x=0): self.x = x
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| 116 | def m1(self, x): self.x = x
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| 117 | def m2(self, y): return self.x + y
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| 118 | __trace_output__ = sys.stdout
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| 119 | class D(C):
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| 120 | def m2(self, y): print "D.m2(%r)" % (y,); return C.m2(self, y)
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| 121 | __trace_output__ = None
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| 122 | x = C(4321)
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| 123 | print x
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| 124 | print x.x
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| 125 | print x.m1(100)
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| 126 | print x.m1(10)
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| 127 | print x.m2(33)
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| 128 | print x.m1(5)
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| 129 | print x.m2(4000)
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| 130 | print x.x
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| 131 |
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| 132 | print C.__init__
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| 133 | print C.m2
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| 134 | print D.__init__
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| 135 | print D.m2
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| 136 |
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| 137 | y = D()
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| 138 | print y
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| 139 | print y.m1(10)
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| 140 | print y.m2(100)
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| 141 | print y.x
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| 142 |
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| 143 | if __name__ == '__main__':
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| 144 | _test()
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