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> from dispatch import generic, strategy
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<                     output = _call_with_errors(func, self, *args, **kw)
---
>                     output = _dispatch_error(func, self, errors, *args, **kw)
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>                 try:
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>                 except Exception, errors:
>                     output = _dispatch_error(func, self, errors, *args, **kw)
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>
> def _dispatch_error(error_source, self, errors, *args, **kw):
>     """ Dispatch error.
>
>     Error handler is a function registered via error_handler decorator or
>     the method that triggered the error (hence forth referred to as
>     "old-style").
>     """
> _dispatch_error = generic()(_dispatch_error)
>
> def _oldstyle_error_handling(error_source, self, errors, *args, **kw):
>     """ Dispatch error old-style like. """
>     return _call_with_errors(error_source, self, *args, **kw)
> _oldstyle_error_handling = _dispatch_error.when(strategy.default)(
>                            _oldstyle_error_handling)
>
> def error_handler(handler, dispatch_rules=None):
>     """ Register handler as an error handler for func.
>
>     dispatch_rules can be a string containing an arbitrary logical Python
>     expression to be used as dispatch rule allowing multiple error handlers
>     for a single method.
>
>     error_handler decorator is an invariant.
>     """
>     def register(func):
>         when = "error_source.__name__ == '%s'" % func.__name__
>         if dispatch_rules:
>             when += " and (%s)" % dispatch_rules
>
>         # First argument of _dispatch_error is only used in dispatch rules,
>         # therefore application code need not declare it.
>         def normalize(func):
>             def prepend_arg(error_source, self, errors, *args, **kw):
>                 return func(self, errors, *args, **kw)
>             return prepend_arg
>
>         _dispatch_error.when(when)(normalize(handler))
>         return func
>     return register
>
>
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< __all__ = ["expose", "validate", "redirect",
---
> __all__ = ["expose", "validate", "redirect", "error_handler",