optimize rendering of results by avoiding console.print

[williballenthin]

using line-profiler, I found that functions like render_feature can be fairly expensive, taking many seconds (cumulatively) to emit their results to the terminal. Digging into this further, it seems that rich's console.print() is relatively slow, taking around 100x longer than intermediate string constructions. This means that when we do a lot of little console.print calls on parts of a line then performance is poor.

We can optimize this by constructing complete regions or lines up front, and then flushing to the terminal with console.print. I think that rich's Text.append is still not very fast, but its better than doing a terminal write.

Originally we used a StringIO-based strategy of building a large output document and then flushing it in one go (rich-unaware). We might want to migrate back in this direction a little bit.

[williballenthin]

then again, the output for my test file was a few thousands of lines, which is not the typical case (nor wanted), so maybe this is not really worth spending time on.

[fariss]

Originally we used a StringIO-based strategy of building a large output document and then flushing it in one go (rich-unaware). We might want to migrate back in this direction a little bit.

I think that's feasible. Rich allows capturing output via StringIO.

[williballenthin]

good point. i'm not sure if the performance issue is:

• writing to stdout, or
• the overhead of rich

writing to a console backed by StringIO and then flushing it at the end sounds pretty nice and also easy to try.

[williballenthin]

@fariss turns out we're already using the stdout capture functionality of rich:

capa/capa/render/vverbose.py

Line 476 in 25d82a2

with console.capture() as capture:

I can try doing an explicit StringIO strategy too. Otherwise I'll need to dig into the overhead of rich and see how we can avoid it.

[williballenthin]

using StringIO directly with a console instance didn't make a meaningful difference in runtime. Therefore, my suspicion is that rich's console.print is expensive, but I need to dig into this and prove it (and why).

[fariss]

The assessment about console.print() being relatively slow is probably correct (a console.print() call has to parse style markups, compute ANSI color codes, ... etc).