RecursionError: maximum recursion depth exceeded for large models

[Osburg]

Hi :)

I ran into the following error. When I try to create a Formula object with more than 246 model terms I get a RecursionError. One can fix this by simply setting the recursion limit to a higher value but I wanted to report this because I think it is potentially unwanted behaviour. This is a minimal example to reproduce the error:

from formulaic import Formula

expr = ""
for i in range(247):
    expr += f"x{i} + "
expr = expr[:-3]

f = Formula(expr)

[matthewwardrop]

Thanks for reporting this @Osburg ! The threshold seems to be much higher for me (737), but I can reproduce this. The issue is that the AST generated for the formula is evaluated implicitly via recursion. Fixing this will require switching to a topological evaluation of the formula, and slightly less clean code. Nevertheless, you're right... this is something that really ought not to break, so I'll see if I can resolve it in 0.4.0.

[matthewwardrop]

The above PR should fix things. My plan is to get it in along with a few other fixes and call it 0.4.0 :).

[matthewwardrop]

@Osburg @DavidWalz Sorry for the delay! 0.4.0 has now been released :).

[DavidWalz]

Awesome, works like a charm!