wrappers.py

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# This file is part of pex_exceptions.
#
# Developed for the LSST Data Management System.
# This product includes software developed by the LSST Project
# (https://www.lsst.org).
# See the COPYRIGHT file at the top-level directory of this distribution
# for details of code ownership.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

__all__ = ["register", "ExceptionMeta", "Exception", "LogicError",
           "DomainError", "InvalidParameterError", "LengthError",
           "OutOfRangeError", "RuntimeError", "RangeError", "OverflowError",
           "UnderflowError", "NotFoundError", "IoError", "TypeError",
           "translate", "declare"]

import warnings

from . import exceptions

registry = {}


def register(cls):
    """A Python decorator that adds a Python exception wrapper to the registry that maps C++ Exceptions
    to their Python wrapper classes.
    """
    registry[cls.WrappedClass] = cls
    return cls


class ExceptionMeta(type):
    """A metaclass for custom exception wrappers, which adds lookup of class attributes
    by delegating to the Swig-generated wrapper.
    """

    def __getattr__(cls, name):
        return getattr(cls.WrappedClass, name)


@register
class Exception(Exception, metaclass=ExceptionMeta):
    """The base class for Python-wrapped LSST C++ exceptions.
    """

    # wrappers.py is an implementation detail, not a public namespace, so we pretend this is defined
    # in the package for pretty-printing purposes
    __module__ = "lsst.pex.exceptions"

    WrappedClass = exceptions.Exception

    def __init__(self, arg, *args, **kwds):
        if isinstance(arg, exceptions.Exception):
            cpp = arg
            message = cpp.what()
        else:
            message = arg
            cpp = self.WrappedClass(message, *args, **kwds)
        super(Exception, self).__init__(message)
        self.cpp = cpp

    def __getattr__(self, name):
        return getattr(self.cpp, name)

    def __repr__(self):
        return "%s('%s')" % (type(self).__name__, self.cpp.what())

    def __str__(self):
        return self.cpp.asString()


@register
class LogicError(Exception):
    WrappedClass = exceptions.LogicError


@register
class DomainError(LogicError):
    WrappedClass = exceptions.DomainError


@register
class InvalidParameterError(LogicError):
    WrappedClass = exceptions.InvalidParameterError


@register
class LengthError(LogicError):
    WrappedClass = exceptions.LengthError


@register
class OutOfRangeError(LogicError):
    WrappedClass = exceptions.OutOfRangeError


@register
class RuntimeError(Exception, RuntimeError):
    WrappedClass = exceptions.RuntimeError


@register
class RangeError(RuntimeError):
    WrappedClass = exceptions.RangeError


@register
class OverflowError(RuntimeError, OverflowError):
    WrappedClass = exceptions.OverflowError


@register
class UnderflowError(RuntimeError, ArithmeticError):
    WrappedClass = exceptions.UnderflowError


@register
class NotFoundError(Exception, LookupError):
    WrappedClass = exceptions.NotFoundError


@register
class IoError(RuntimeError, IOError):
    WrappedClass = exceptions.IoError


@register
class TypeError(LogicError, TypeError):
    WrappedClass = exceptions.TypeError


def translate(cpp):
    """Translate a C++ Exception instance to Python and return it."""
    PyType = registry.get(type(cpp), None)
    if PyType is None:
        warnings.warn("Could not find appropriate Python type for C++ Exception")
        PyType = Exception
    return PyType(cpp)


def declare(module, exception_name, base, wrapped_class):
    """Declare a new exception."""
    setattr(module, exception_name, register(ExceptionMeta(exception_name, (base, ),
                                                           dict(WrappedClass=wrapped_class))))