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{- arch-tag: Python low-level exception handling
Copyright (C) 2005 John Goerzen <jgoerzen@complete.org>
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 2 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, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
-}
{- |
Module : Python.Exceptions
Copyright : Copyright (C) 2005 John Goerzen
License : GNU GPL, version 2 or above
Maintainer : John Goerzen,
Maintainer : jgoerzen\@complete.org
Stability : provisional
Portability: portable
Python low-level exception handling
Written by John Goerzen, jgoerzen\@complete.org
-}
module Python.Exceptions (-- * Types
PyException(..),
-- * General Catching
catchPy,
handlePy,
pyExceptions,
-- * Catching of specific Python exceptions
catchSpecificPy,
-- * Exception Object Operations
formatException,
doesExceptionMatch,
-- * Re-Raising Exceptions
exc2ioerror
)
where
import Python.Utils
import Foreign.C.Types
import Python.Objects
import Foreign
import Python.Types
import Data.Dynamic
import Data.Typeable
import Control.Exception
import Python.Interpreter
import Python.ForeignImports
{- | Execute the given IO action.
If it raises a 'PyException', then execute the supplied handler and return
its return value. Otherwise, process as normal. -}
catchPy :: IO a -> (PyException -> IO a) -> IO a
catchPy = catchDyn
{- | Like 'catchPy', with the order of arguments reversed. -}
handlePy :: (PyException -> IO a) -> IO a -> IO a
handlePy = flip catchPy
{- | Like catchPy, but catches only instances of the Python class given
(see 'doesExceptionMatch'). -}
catchSpecificPy :: PyObject -> IO a -> (PyException -> IO a) -> IO a
catchSpecificPy pyo action handlerfunc =
let handler e = do d <- doesExceptionMatch e pyo
if d
then handlerfunc e
else throwDyn e
in catchPy action handler
{- | Useful as the first argument to catchJust, tryJust, or handleJust.
Return Nothing if the given exception is not a 'PyException', or
the exception otherwise. -}
pyExceptions :: Exception -> Maybe PyException
pyExceptions exc = dynExceptions exc >>= fromDynamic
{- | When an exception is thrown, it is not immediately formatted.
This call will format it. -}
formatException :: PyException -> IO PyException
formatException e =
{-
do fmt <- callByName "traceback.format_exception"
[excType e, excValue e, excTraceBack e] [] >>= fromPyObject
-}
do ename <- strOf (excType e)
evalue <- strOf (excValue e)
let fmt = ename ++ ": " ++ evalue
return $ e {excFormatted = fmt}
{- | Returns true if the passed 'PyException' matches the given Python
exception class or one of its subclasses. Standard Python exception classes
are given in 'Python.Exceptions.ExcTypes'. -}
doesExceptionMatch :: PyException -> PyObject -> IO Bool
doesExceptionMatch e pyo =
withPyObject (excType e) (\ctyp ->
withPyObject pyo (\cpo ->
do r <- pyErr_GivenExceptionMatches ctyp cpo >>= checkCInt
if r == 0
then return False
else return True
))
{- | A handler for use in 'catchPy' or 'handlePy'. Grabs the Python exception,
describes it, and raises the description in the IO monad with 'fail'. -}
exc2ioerror :: PyException -> IO a
exc2ioerror e = do e2 <- formatException e
fail $ "Python " ++ show e2
|
