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()
145