Edit: exception.py
# Copyright (C) 2003-2007, 2009-2011 Nominum, Inc. # # Permission to use, copy, modify, and distribute this software and its # documentation for any purpose with or without fee is hereby granted, # provided that the above copyright notice and this permission notice # appear in all copies. # # THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES # WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF # MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR # ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES # WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN # ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT # OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. """Common DNS Exceptions.""" class DNSException(Exception): """Abstract base class shared by all dnspython exceptions. It supports two basic modes of operation: a) Old/compatible mode is used if __init__ was called with empty **kwargs. In compatible mode all *args are passed to standard Python Exception class as before and all *args are printed by standard __str__ implementation. Class variable msg (or doc string if msg is None) is returned from str() if *args is empty. b) New/parametrized mode is used if __init__ was called with non-empty **kwargs. In the new mode *args has to be empty and all kwargs has to exactly match set in class variable self.supp_kwargs. All kwargs are stored inside self.kwargs and used in new __str__ implementation to construct formatted message based on self.fmt string. In the simplest case it is enough to override supp_kwargs and fmt class variables to get nice parametrized messages. """ msg = None # non-parametrized message supp_kwargs = set() # accepted parameters for _fmt_kwargs (sanity check) fmt = None # message parametrized with results from _fmt_kwargs def __init__(self, *args, **kwargs): self._check_params(*args, **kwargs) if kwargs: self.kwargs = self._check_kwargs(**kwargs) self.msg = str(self) else: self.kwargs = dict() # defined but empty for old mode exceptions if self.msg is None: # doc string is better implicit message than empty string self.msg = self.__doc__ if args: super(DNSException, self).__init__(*args) else: super(DNSException, self).__init__(self.msg) def _check_params(self, *args, **kwargs): """Old exceptions supported only args and not kwargs. For sanity we do not allow to mix old and new behavior.""" if args or kwargs: assert bool(args) != bool(kwargs), \ 'keyword arguments are mutually exclusive with positional args' def _check_kwargs(self, **kwargs): if kwargs: assert set(kwargs.keys()) == self.supp_kwargs, \ 'following set of keyword args is required: %s' % ( self.supp_kwargs) return kwargs def _fmt_kwargs(self, **kwargs): """Format kwargs before printing them. Resulting dictionary has to have keys necessary for str.format call on fmt class variable. """ fmtargs = {} for kw, data in kwargs.items(): if isinstance(data, (list, set)): # convert list of <someobj> to list of str(<someobj>) fmtargs[kw] = list(map(str, data)) if len(fmtargs[kw]) == 1: # remove list brackets [] from single-item lists fmtargs[kw] = fmtargs[kw].pop() else: fmtargs[kw] = data return fmtargs def __str__(self): if self.kwargs and self.fmt: # provide custom message constructed from keyword arguments fmtargs = self._fmt_kwargs(**self.kwargs) return self.fmt.format(**fmtargs) else: # print *args directly in the same way as old DNSException return super(DNSException, self).__str__() class FormError(DNSException): """DNS message is malformed.""" class SyntaxError(DNSException): """Text input is malformed.""" class UnexpectedEnd(SyntaxError): """Text input ended unexpectedly.""" class TooBig(DNSException): """The DNS message is too big.""" class Timeout(DNSException): """The DNS operation timed out.""" supp_kwargs = set(['timeout']) fmt = "The DNS operation timed out after {timeout} seconds"
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