--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/symbian-qemu-0.9.1-12/python-2.6.1/Demo/metaclasses/Trace.py	Fri Jul 31 15:01:17 2009 +0100
@@ -0,0 +1,144 @@
+"""Tracing metaclass.
+
+XXX This is very much a work in progress.
+
+"""
+
+import types, sys
+
+class TraceMetaClass:
+    """Metaclass for tracing.
+
+    Classes defined using this metaclass have an automatic tracing
+    feature -- by setting the __trace_output__ instance (or class)
+    variable to a file object, trace messages about all calls are
+    written to the file.  The trace formatting can be changed by
+    defining a suitable __trace_call__ method.
+
+    """
+
+    __inited = 0
+
+    def __init__(self, name, bases, dict):
+        self.__name__ = name
+        self.__bases__ = bases
+        self.__dict = dict
+        # XXX Can't define __dict__, alas
+        self.__inited = 1
+
+    def __getattr__(self, name):
+        try:
+            return self.__dict[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.__dict[name] = value
+
+    def __call__(self, *args, **kw):
+        inst = TracingInstance()
+        inst.__meta_init__(self)
+        try:
+            init = inst.__getattr__('__init__')
+        except AttributeError:
+            init = lambda: None
+        apply(init, args, kw)
+        return inst
+
+    __trace_output__ = None
+
+class TracingInstance:
+    """Helper class to represent an instance of a tracing class."""
+
+    def __trace_call__(self, fp, fmt, *args):
+        fp.write((fmt+'\n') % args)
+
+    def __meta_init__(self, klass):
+        self.__class = klass
+
+    def __getattr__(self, name):
+        # Invoked for any attr not in the instance's __dict__
+        try:
+            raw = self.__class.__getattr__(name)
+        except AttributeError:
+            raise AttributeError, name
+        if type(raw) != types.FunctionType:
+            return raw
+        # It's a function
+        fullname = self.__class.__name__ + "." + name
+        if not self.__trace_output__ or name == '__trace_call__':
+            return NotTracingWrapper(fullname, raw, self)
+        else:
+            return TracingWrapper(fullname, raw, self)
+
+class NotTracingWrapper:
+    def __init__(self, name, func, inst):
+        self.__name__ = name
+        self.func = func
+        self.inst = inst
+    def __call__(self, *args, **kw):
+        return apply(self.func, (self.inst,) + args, kw)
+
+class TracingWrapper(NotTracingWrapper):
+    def __call__(self, *args, **kw):
+        self.inst.__trace_call__(self.inst.__trace_output__,
+                                 "calling %s, inst=%s, args=%s, kw=%s",
+                                 self.__name__, self.inst, args, kw)
+        try:
+            rv = apply(self.func, (self.inst,) + args, kw)
+        except:
+            t, v, tb = sys.exc_info()
+            self.inst.__trace_call__(self.inst.__trace_output__,
+                                     "returning from %s with exception %s: %s",
+                                     self.__name__, t, v)
+            raise t, v, tb
+        else:
+            self.inst.__trace_call__(self.inst.__trace_output__,
+                                     "returning from %s with value %s",
+                                     self.__name__, rv)
+            return rv
+
+Traced = TraceMetaClass('Traced', (), {'__trace_output__': None})
+
+
+def _test():
+    global C, D
+    class C(Traced):
+        def __init__(self, x=0): self.x = x
+        def m1(self, x): self.x = x
+        def m2(self, y): return self.x + y
+        __trace_output__ = sys.stdout
+    class D(C):
+        def m2(self, y): print "D.m2(%r)" % (y,); return C.m2(self, y)
+        __trace_output__ = None
+    x = C(4321)
+    print x
+    print x.x
+    print x.m1(100)
+    print x.m1(10)
+    print x.m2(33)
+    print x.m1(5)
+    print x.m2(4000)
+    print x.x
+
+    print C.__init__
+    print C.m2
+    print D.__init__
+    print D.m2
+
+    y = D()
+    print y
+    print y.m1(10)
+    print y.m2(100)
+    print y.x
+
+if __name__ == '__main__':
+    _test()