Optimization on load

[simoncozens]

Some OT tables rely on "aux" fields which are conditions written as strings; a classic example is the Device field which has the condition "DeltaFormat in (1,2,3)". This is currently stored as a string in the Convertor object, and is evaled for each Device table it decompiles.

eval is very slow. You can get a small speedup - quite a large speedup for fonts with lots of Device/VariationIndex tables - by compiling the string and evaling the compiled version later.

[simoncozens]

Thank you! Here's a font with a particularly large GPOS table:

font = TTFont("Bigfont.ttf")
count = len(font["GPOS"].table.LookupList.Lookup)
print(f"I have {count} GPOS lookups")

Before:

$ time python3 open.py
I have 46 GPOS lookups
python3 open.py  3.07s user 0.06s system 98% cpu 3.161 total

After:

$ time PYTHONPATH=Lib python3 open.py
I have 46 GPOS lookups
PYTHONPATH=Lib python3 open.py  2.29s user 0.05s system 99% cpu 2.355 total

[anthrotype]

thanks. A test would also have been nice, to confirm this trick works reliably on all the pythons we support.

[simoncozens]

That's what the existing test suite is for...

[anthrotype]

thanks for confirming that the changes are covered by our current test suite