"Attempt to retrieve context when no valid context" when calling glVertexAttribPointer in GL ES 2

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I have a program (http://vectorpoem.com/playscii) that's been running
nicely with PyOpenGL on x86 Linux, macOS, and Windows for a few years now,
and I'm now attempting to get it running on a Raspberry Pi 3 (using the
Raspbian OpenGL driver). Until now this process was pretty straightforward,
tweaking shaders and providing a render path for non-VAO hardware, but I've
now hit a crash I don't understand and can't figure out how to debug.

Deep into program initialization, I'm setting up some vertex buffers, and
get a crash whose final line is "OpenGL.error.Error: Attempt to retrieve
context when no valid context" when calling glVertexAttribPointer. See the
full log here; my program first logs info about the hardware and the OpenGL
context it creates (via PySDL2), followed by the crash:

https://gist.github.com/JPLeBreton/782b92872380ee6ab3b11b3954ca56cd

The OpenGL render context is definitely present; I tried logging stuff
about it just before the glVertexAttribPointer call and as far as I can
tell it's valid right up until that point. For what it's worth that call
does appear to be the first (of many) in the program's execution.

Happy to provide more info as needed. Thanks.

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<div dir=3D"auto"><div dir=3D"ltr">I have a program (<a href=3D"http://vect=
orpoem.com/playscii" target=3D"_blank">http://vectorpoem.com/<wbr>playscii<=
/a>) that&#39;s been running nicely with PyOpenGL on x86 Linux, macOS, and =
Windows for a few years now, and I&#39;m now attempting to get it running o=
n a Raspberry Pi 3 (using the Raspbian OpenGL driver). Until now this proce=
ss was pretty straightforward, tweaking shaders and providing a render path=
 for non-VAO hardware, but I&#39;ve now hit a crash I don&#39;t understand =
and can&#39;t figure out how to debug.<br><br>Deep into program initializat=
ion, I&#39;m setting up some vertex buffers, and get a crash whose final li=
ne is &quot;OpenGL.error.Error: Attempt to retrieve context when no valid c=
ontext&quot; when calling glVertexAttribPointer. See the full log here; my =
program first logs info about the hardware and the OpenGL context it create=
s (via PySDL2), followed by the crash:<br><br><a href=3D"https://gist.githu=
b.com/JPLeBreton/782b92872380ee6ab3b11b3954ca56cd" target=3D"_blank">https:=
//gist.github.com/<wbr>JPLeBreton/<wbr>782b92872380ee6ab3b11b3954ca56<wbr>c=
d</a><br><br>The OpenGL render context is definitely present; I tried loggi=
ng stuff about it just before the glVertexAttribPointer call and as far as =
I can tell it&#39;s valid right up until that point. For what it&#39;s wort=
h that call does appear to be the first (of many) in the program&#39;s exec=
ution.<br></div><div dir=3D"ltr"><br></div><div dir=3D"ltr">Happy to provid=
e more info as needed. Thanks.</div></div>

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