/py/_error.py

"""
create errno-specific classes for IO or os calls.

"""
import sys, os, errno

class Error(EnvironmentError):
    def __repr__(self):
        return "%s.%s %r: %s " %(self.__class__.__module__,
                               self.__class__.__name__,
                               self.__class__.__doc__,
                               " ".join(map(str, self.args)),
                               #repr(self.args)
                                )

    def __str__(self):
        s = "[%s]: %s" %(self.__class__.__doc__,
                          " ".join(map(str, self.args)),
                          )
        return s

_winerrnomap = {
    2: errno.ENOENT,
    3: errno.ENOENT,
    17: errno.EEXIST,
    13: errno.EBUSY, # empty cd drive, but ENOMEDIUM seems unavailiable
    22: errno.ENOTDIR,
    267: errno.ENOTDIR,
    5: errno.EACCES,  # anything better?
}

class ErrorMaker(object):
    """ lazily provides Exception classes for each possible POSIX errno
        (as defined per the 'errno' module).  All such instances
        subclass EnvironmentError.
    """
    Error = Error
    _errno2class = {}

    def __getattr__(self, name):
        if name[0] == "_":
            raise AttributeError(name)
        eno = getattr(errno, name)
        cls = self._geterrnoclass(eno)
        setattr(self, name, cls)
        return cls

    def _geterrnoclass(self, eno):
        try:
            return self._errno2class[eno]
        except KeyError:
            clsname = errno.errorcode.get(eno, "UnknownErrno%d" %(eno,))
            errorcls = type(Error)(clsname, (Error,),
                    {'__module__':'py.error',
                     '__doc__': os.strerror(eno)})
            self._errno2class[eno] = errorcls
            return errorcls

    def checked_call(self, func, *args, **kwargs):
        """ call a function and raise an errno-exception if applicable. """
        __tracebackhide__ = True
        try:
            return func(*args, **kwargs)
        except self.Error:
            raise
        except EnvironmentError:
            cls, value, tb = sys.exc_info()
            if not hasattr(value, 'errno'):
                raise
            __tracebackhide__ = False
            errno = value.errno
            try:
                if not isinstance(value, WindowsError):
                    raise NameError
            except NameError:
                # we are not on Windows, or we got a proper OSError
                cls = self._geterrnoclass(errno)
            else:
                try:
                    cls = self._geterrnoclass(_winerrnomap[errno])
                except KeyError:
                    raise value
            raise cls("%s%r" % (func.__name__, args))
            __tracebackhide__ = True

error = ErrorMaker()