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Filename : exception.py
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# 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"