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from sqlalchemy import util
def listen(fn, identifier, target, *args):
"""Listen for events, passing to fn."""
target._dispatch.append(fn, identifier, target, *args)
NO_RESULT = util.symbol('no_result')
class Dispatch(object):
def append(self, identifier, fn, target):
getattr(self, identifier).append(fn)
def __getattr__(self, key):
self.__dict__[key] = coll = []
return coll
def chain(self, identifier, chain_kw, **kw):
ret = NO_RESULT
for fn in getattr(self, identifier):
ret = fn(**kw)
kw['chain_kw'] = ret
return ret
def __call__(self, identifier, **kw):
for fn in getattr(self, identifier):
fn(**kw)
class dispatcher(object):
def __init__(self, dispatch_cls=Dispatch):
self.dispatch_cls = dispatch_cls
self._dispatch = dispatch_cls()
def __get__(self, obj, cls):
if obj is None:
return self._dispatch
obj.__dict__['_dispatch'] = disp = self.dispatch_cls()
for key in self._dispatch.__dict__:
if key.startswith('on_'):
disp.__dict__[key] = self._dispatch.__dict__[k].copy()
return disp
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