Current File : //lib64/python2.7/Demo/metaclasses/Trace.py
"""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()
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