| Guido van Rossum | bff110f | 1997-08-23 21:14:37 +0000 | [diff] [blame^] | 1 | """Tracing metaclass.""" |
| 2 | |
| 3 | import types |
| 4 | |
| 5 | class TraceMetaClass: |
| 6 | """Metaclass for tracing. |
| 7 | |
| 8 | Classes defined using this metaclass have an automatic tracing |
| 9 | feature -- by setting the __trace_output__ instance (or class) |
| 10 | variable to a file object, trace messages about all calls are |
| 11 | written to the file. The trace formatting can be changed by |
| 12 | defining a suitable __trace_call__ method. |
| 13 | |
| 14 | """ |
| 15 | |
| 16 | __inited = 0 |
| 17 | |
| 18 | def __init__(self, name, bases, dict): |
| 19 | self.__name__ = name |
| 20 | self.__bases__ = bases |
| 21 | self.__dict = dict |
| 22 | # XXX Can't define __dict__, alas |
| 23 | self.__inited = 1 |
| 24 | |
| 25 | def __getattr__(self, name): |
| 26 | try: |
| 27 | return self.__dict[name] |
| 28 | except KeyError: |
| 29 | for base in self.__bases__: |
| 30 | try: |
| 31 | return getattr(base, name) |
| 32 | except AttributeError: |
| 33 | pass |
| 34 | raise AttributeError, name |
| 35 | |
| 36 | def __setattr__(self, name, value): |
| 37 | if not self.__inited: |
| 38 | self.__dict__[name] = value |
| 39 | else: |
| 40 | self.__dict[name] = value |
| 41 | |
| 42 | def __call__(self, *args, **kw): |
| 43 | inst = TracingInstance() |
| 44 | inst.__meta_init__(self) |
| 45 | try: |
| 46 | init = inst.__getattr__('__init__') |
| 47 | except AttributeError: |
| 48 | init = lambda: None |
| 49 | apply(init, args, kw) |
| 50 | return inst |
| 51 | |
| 52 | __trace_output__ = None |
| 53 | |
| 54 | class TracingInstance: |
| 55 | """Helper class to represent an instance of a tracing class.""" |
| 56 | |
| 57 | def __trace_call__(self, fp, fmt, *args): |
| 58 | fp.write((fmt+'\n') % args) |
| 59 | |
| 60 | def __meta_init__(self, klass): |
| 61 | self.__class = klass |
| 62 | |
| 63 | def __getattr__(self, name): |
| 64 | # Invoked for any attr not in the instance's __dict__ |
| 65 | try: |
| 66 | raw = self.__class.__getattr__(name) |
| 67 | except AttributeError: |
| 68 | raise AttributeError, name |
| 69 | if type(raw) != types.FunctionType: |
| 70 | return raw |
| 71 | # It's a function |
| 72 | fullname = self.__class.__name__ + "." + name |
| 73 | if not self.__trace_output__ or name == '__trace_call__': |
| 74 | return NotTracingWrapper(fullname, raw, self) |
| 75 | else: |
| 76 | return TracingWrapper(fullname, raw, self) |
| 77 | |
| 78 | class NotTracingWrapper: |
| 79 | def __init__(self, name, func, inst): |
| 80 | self.__name__ = name |
| 81 | self.func = func |
| 82 | self.inst = inst |
| 83 | def __call__(self, *args, **kw): |
| 84 | return apply(self.func, (self.inst,) + args, kw) |
| 85 | |
| 86 | class TracingWrapper(NotTracingWrapper): |
| 87 | def __call__(self, *args, **kw): |
| 88 | self.inst.__trace_call__(self.inst.__trace_output__, |
| 89 | "calling %s, inst=%s, args=%s, kw=%s", |
| 90 | self.__name__, self.inst, args, kw) |
| 91 | try: |
| 92 | rv = apply(self.func, (self.inst,) + args, kw) |
| 93 | except: |
| 94 | t, v, tb = sys.exc_info() |
| 95 | self.inst.__trace_call__(self.inst.__trace_output__, |
| 96 | "returning from %s with exception %s: %s", |
| 97 | self.__name__, t, v) |
| 98 | raise t, v, tb |
| 99 | else: |
| 100 | self.inst.__trace_call__(self.inst.__trace_output__, |
| 101 | "returning from %s with value %s", |
| 102 | self.__name__, rv) |
| 103 | return rv |
| 104 | |
| 105 | Traced = TraceMetaClass('Traced', (), {'__trace_output__': None}) |
| 106 | |
| 107 | |
| 108 | def _test(): |
| 109 | import sys |
| 110 | class C(Traced): |
| 111 | def __init__(self, x=0): self.x = x |
| 112 | def m1(self, x): self.x = x |
| 113 | def m2(self, y): return self.x + y |
| 114 | C.__trace_output__ = sys.stdout |
| 115 | x = C(4321) |
| 116 | print x |
| 117 | print x.x |
| 118 | print x.m1(100) |
| 119 | print x.m1(10) |
| 120 | print x.m2(33) |
| 121 | print x.m1(5) |
| 122 | print x.m2(4000) |
| 123 | print x.x |
| 124 | |
| 125 | if __name__ == '__main__': |
| 126 | _test() |