I've recently started using this library to get at structured RandR information. It's been really easy to jump in and start working with but couldn't find a way to get at the screen refresh rate information.

After a bit of searching around and reading up on XRandR I noticed that the xrandr_get_screen_info() function is what I was interested in but it looks like the refresh rates list is currently tagged with a FIXME.

I did a bit of debugging/reading and figured out that:

• The refresh rate list was added in version 1.2 (?) (requires call to xrandr_query_version())
• The sub-lists are not 32-bit aligned (requires removing padding to unpack correctly)

I was able to get it working with the below changes (admittedly I have not tested the code extensively but simply setting the pad argument to 0 appears to extract the list without breaking backwards compatibility).

diff --git a/Xlib/ext/randr.py b/Xlib/ext/randr.py
index 0a1dfb9..c15ec95 100644
--- a/Xlib/ext/randr.py
+++ b/Xlib/ext/randr.py
@@ -151,7 +151,7 @@ RandR_ModeInfo = rq.Struct(
 
 RandR_Rates = rq.Struct(
         rq.LengthOf('rates', 2),
-        rq.List('rates', rq.Card16Obj)
+        rq.List('rates', rq.Card16Obj, pad = 0)
         )
 
 # TODO: This struct is part of the RENDER extension and should be moved there
@@ -323,7 +323,7 @@ class GetScreenInfo(rq.ReplyRequest):
         rq.Card16('n_rate_ents'), # XCB's protocol description disagrees with the X headers on this; ignoring.
         rq.Pad(2),
         rq.List('sizes', RandR_ScreenSizes),
-        #rq.List('rates', RandR_Rates) #FIXME: Why does uncommenting this cause an error?
+        rq.List('rates', RandR_Rates)
         )
 
 def get_screen_info(self):

I am still very new to this code base, Xrandr and the X Server Protocol in general so I'm not sure if this could cause issues elsewhere. This method doesn't get the size of the refresh rate list ahead of time and I toyed with the idea of using either the length of the size list or n_rate_ents to compute the length but this feels cleaner and safer.

Hoping to get a second opinion or see if this fix might be considered.

Quick example of getting the rates from root screen (both with "initial" and latest version of Xrandr):

Python 3.7.3 (default, Mar 26 2019, 21:43:19) 
[GCC 8.2.1 20181127] on linux
Type "help", "copyright", "credits" or "license" for more information.
+>>> from Xlib import display
+>>> from Xlib.ext import randr
+>>> import pprint
+>>> d = display.Display()
+>>> d.screen().root.xrandr_get_screen_info().rates
[]
+>>> d.xrandr_query_version()
<<class 'Xlib.ext.randr.QueryVersion'> serial = 15, data = {'sequence_number': 15, 'major_version': 1, 'minor_version': 3}, error = None>
+>>> pprint.pprint([ r._data for r in d.screen().root.xrandr_get_screen_info().rates ])
[{'rates': [60]},
 {'rates': [60]},
 {'rates': [60]},
 {'rates': [60]},
 {'rates': [60]},
 {'rates': [60]},
 {'rates': [60]},
 {'rates': [60]},
 {'rates': [60, 56]},
 {'rates': [60]},
 {'rates': [60]},
 {'rates': [60]},
 {'rates': [60, 59]},
 {'rates': [60, 59]},
 {'rates': []}]
+>>>