Re: [Libguestfs] [PATCH libnbd v3] python: Raise a custom exception containing error string and errno.

On 6/28/19 1:27 PM, Richard W.M. Jones wrote: > Previously errors caused a RuntimeException to be raised. This commit > defines a custom exception (nbd.Error) which has two parameters, the > required error string, and the optional errno (which may be 0 if > unavailable). > > For example: > > $ ./run nbdsh -c 'h.pread(0, 0)' > Traceback (most recent call last): > File "/usr/lib64/python3.7/runpy.py", line 193, in _run_module_as_main > "__main__", mod_spec) > File "/usr/lib64/python3.7/runpy.py", line 85, in _run_code > exec(code, run_globals) > File "/home/rjones/d/libnbd/python/nbd.py", line 1163, in <module> > nbdsh.shell() > File "/home/rjones/d/libnbd/python/nbdsh.py", line 62, in shell > exec (c) > File "<string>", line 1, in <module> > File "/home/rjones/d/libnbd/python/nbd.py", line 483, in pread > return libnbdmod.pread (self._o, count, offset, flags) > nbd.Error: nbd_pread: invalid state: START: the handle must be connected and finished handshaking with the server: Transport endpoint is not connected (ENOTCONN) Cool - in the time I spent writing my reply to v2 1/1, your reaction to my reply on 0/1 figured out the way to get what we want: > @@ -3917,6 +3938,36 @@ Read the libnbd(3) man page to find out how to use the API. > > import libnbdmod > > +# Re-export Error exception as nbd.Error, adding some methods. > +from libnbdmod import Error Implement all the cool stuff in pure Python on top of the bare-bones minimum :) Lots less hassle than writing it in C code. I like it! > + > +Error.__doc__ = ''' > +Exception thrown when the underlying libnbd call fails. > + > +This exception has two properties to query the error. Use > +the .string property to return a printable string containing > +the error message. Use the .errno property to return a > +Python errno (which may be None in some cases if the error > +did not correspond to a system call failure). > +''' > + > +Error.string = property (lambda self: self.args[0]) > + > +def _errno (self): > + import errno > + try: > + return errno.errorcode[self.args[1]] > + except KeyError: > + return None > +Error.errno = property (_errno) > + > +def _str (self): > + if self.errno: > + return (\"%%s (%%s)\" %% (self.string, self.errno)) > + else: > + return (\"%%s\" %% self.string) > +Error.__str__ = _str Looks good to me now! Thanks for figuring this out while I was struggling with reading lots of documentation on C bindings. ACK