从python中的键代码获取keyym

Question

I am currently working on a python project to enable the detection and interpretation of key events as characters/names across platforms. I have been working with python-xlib to provide support on X11 but I have recently run into difficulty in the process of converting the keycodes of key events to their appropriate keysyms.

A snapshot of my code is here: https://gist.github.com/SavinaRoja/7306962

The trouble arises specifically in the use of the PyKeyboardEvent class, where I am capable of retrieving the event data for key events, but not interpreting their keycodes to keysyms. Xlib.display's keycode_to_keysym function does not work appropriately.

In reading about X11, and confirmed by the xev utility source code, it seems that the appropriate Xlib function to utilize is XLookupString. Were I coding in C (a language I am only beginning to learn) using this function would be simple, however I am currently stumped with regards to employing the function from python. I have considered two options: I may attempt to utilize and extend python-xlib's protocol to call XLookupString, or I might try to use ctypes to call XLookupString. My code includes an attempt at the latter (not functional, but shows where I am at currently):

from ctypes import *
XLookupString = cdll.LoadLibrary('libX11.so').XLookupString

char_buffer = create_string_buffer(257)
keysym = c_int()  # the important value
count = XLookupString(byref(event),  # TypeError, not a ctypes instance
                      byref(char_buffer),
                      len(char_buffer),
                      keysym,
                      None)

I suspect that what I am missing is the ability to convert the event class from python-xlib to an appropriate C struct for XLookupString, or the ability to interpret the data received from the X server (which python-xlib parses into the event instance) into such a struct. Am I correct in this suspicion? If so, what tools do I need to learn?

At this point I am probably missing a lot of basic information and skill regarding the interface between python and C, so I devoting time to fixing this gap in my general education. If anyone has insight in to my problem specifically or how I should conduct my research on relevant topics, I would love to hear it.

Answer 1

If you look at the source code to python-xlib, it's actually not using xlib at all; it's a pure-Python implementation of the Xlib socket protocols. You event object is a wrapper around one of the types defined in the rq module (or a subclass defined in event or elsewhere), which is an object that knows how to struct.pack itself.

The simplest thing to do is probably to pack the value into a byte string, then cast it to a ctypes.Structure .

But note that the xlib that ctypes will be entirely independent of your python-xlib ; in particular, you'll be using a different X connection (which means you may have to auth separately, repeat any setup, etc.). It would probably be a lot cleaner to do everything one way or the other, not mix and match.

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Downloading the libX11 source , it looks like XLookupString is not a protocol function, but rather a wrapper (in the file KeyBind.c ) that runs at least partially on the client side. Assuming USE_OWN_COMPOSE is not defined, it effectively calls XTranslateKey to get the keysym result, then calls XTranslateKeySym to fill the string buffer. Those functions are themselves mostly local functions. But they ultimately call XKeyInitialize , which calls at least one server-side function, XGetKeyboardMapping —which python-xlib does support.

That implies that using a separate Xlib instance through ctypes is not necessarily going to get the right keyboard mapping, unless you can ensure that the two connections have identical setup.

That also implies that you may have to port all of that local C code in order to get the functionality of XLookupString .