/Demo/metaclasses/Trace.py

  1"""Tracing metaclass.
  2
  3XXX This is very much a work in progress.
  4
  5"""
  6
  7import types, sys
  8
  9class TraceMetaClass:
 10    """Metaclass for tracing.
 11
 12    Classes defined using this metaclass have an automatic tracing
 13    feature -- by setting the __trace_output__ instance (or class)
 14    variable to a file object, trace messages about all calls are
 15    written to the file.  The trace formatting can be changed by
 16    defining a suitable __trace_call__ method.
 17
 18    """
 19
 20    __inited = 0
 21
 22    def __init__(self, name, bases, dict):
 23        self.__name__ = name
 24        self.__bases__ = bases
 25        self.__dict = dict
 26        # XXX Can't define __dict__, alas
 27        self.__inited = 1
 28
 29    def __getattr__(self, name):
 30        try:
 31            return self.__dict[name]
 32        except KeyError:
 33            for base in self.__bases__:
 34                try:
 35                    return base.__getattr__(name)
 36                except AttributeError:
 37                    pass
 38            raise AttributeError, name
 39
 40    def __setattr__(self, name, value):
 41        if not self.__inited:
 42            self.__dict__[name] = value
 43        else:
 44            self.__dict[name] = value
 45
 46    def __call__(self, *args, **kw):
 47        inst = TracingInstance()
 48        inst.__meta_init__(self)
 49        try:
 50            init = inst.__getattr__('__init__')
 51        except AttributeError:
 52            init = lambda: None
 53        apply(init, args, kw)
 54        return inst
 55
 56    __trace_output__ = None
 57
 58class TracingInstance:
 59    """Helper class to represent an instance of a tracing class."""
 60
 61    def __trace_call__(self, fp, fmt, *args):
 62        fp.write((fmt+'\n') % args)
 63
 64    def __meta_init__(self, klass):
 65        self.__class = klass
 66
 67    def __getattr__(self, name):
 68        # Invoked for any attr not in the instance's __dict__
 69        try:
 70            raw = self.__class.__getattr__(name)
 71        except AttributeError:
 72            raise AttributeError, name
 73        if type(raw) != types.FunctionType:
 74            return raw
 75        # It's a function
 76        fullname = self.__class.__name__ + "." + name
 77        if not self.__trace_output__ or name == '__trace_call__':
 78            return NotTracingWrapper(fullname, raw, self)
 79        else:
 80            return TracingWrapper(fullname, raw, self)
 81
 82class NotTracingWrapper:
 83    def __init__(self, name, func, inst):
 84        self.__name__ = name
 85        self.func = func
 86        self.inst = inst
 87    def __call__(self, *args, **kw):
 88        return apply(self.func, (self.inst,) + args, kw)
 89
 90class TracingWrapper(NotTracingWrapper):
 91    def __call__(self, *args, **kw):
 92        self.inst.__trace_call__(self.inst.__trace_output__,
 93                                 "calling %s, inst=%s, args=%s, kw=%s",
 94                                 self.__name__, self.inst, args, kw)
 95        try:
 96            rv = apply(self.func, (self.inst,) + args, kw)
 97        except:
 98            t, v, tb = sys.exc_info()
 99            self.inst.__trace_call__(self.inst.__trace_output__,
100                                     "returning from %s with exception %s: %s",
101                                     self.__name__, t, v)
102            raise t, v, tb
103        else:
104            self.inst.__trace_call__(self.inst.__trace_output__,
105                                     "returning from %s with value %s",
106                                     self.__name__, rv)
107            return rv
108
109Traced = TraceMetaClass('Traced', (), {'__trace_output__': None})
110
111
112def _test():
113    global C, D
114    class C(Traced):
115        def __init__(self, x=0): self.x = x
116        def m1(self, x): self.x = x
117        def m2(self, y): return self.x + y
118        __trace_output__ = sys.stdout
119    class D(C):
120        def m2(self, y): print "D.m2(%r)" % (y,); return C.m2(self, y)
121        __trace_output__ = None
122    x = C(4321)
123    print x
124    print x.x
125    print x.m1(100)
126    print x.m1(10)
127    print x.m2(33)
128    print x.m1(5)
129    print x.m2(4000)
130    print x.x
131
132    print C.__init__
133    print C.m2
134    print D.__init__
135    print D.m2
136
137    y = D()
138    print y
139    print y.m1(10)
140    print y.m2(100)
141    print y.x
142
143if __name__ == '__main__':
144    _test()