C API: Making a context manager

[Stefan Behnel]

Chris Kaynor, 31.10.2011 19:34:
> I am currently rewritting a class using the Python C API to improve
> performance of it, however I have not been able to find any
> documentation about how to make a context manager using the C API.

You should take a look at Cython. It makes these things *so* much easier.


> The code I am working to produce is the following (its a method of a class):
>
> @contextlib.contextmanager
> def connected(self, *args, **kwargs):
> 	connection = self.connect(*args, **kwargs)
> 	try:
> 		yield
> 	finally:
> 		connection.disconnect()

You can use the above in Cython code unmodified, and it's likely going to 
be good enough (depending on what kind of connection we are talking about 
here).

In case that's also performance critical, however, it's likely faster to 
spell it out as a class, i.e.

     ...
         def connected(self, *args, **kwargs):
             return ConnectionManager(self, args, kwargs)


     cdef class ConnectionManager:
         cdef object args, kwargs, connection, connect

         def __init__(self, connector, args, kwargs):
             self.args, self.kwargs = args, kwargs
             self.connect = connector.connect
         def __enter__(self):
             self.connection = self.connect(*self.args, **self.kwargs)
         def __exit__(self, *exc):
             self.connection.disconnect()
             return True # or False? I always forget which means what

Not that much longer either.

Stefan