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

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)

@@ -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

+ +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