pp.ParserElement.enable_left_recursion() gives runtime error

[Hugues Hoppe]

Running this code in a fresh environment:

import pyparsing as pp
print(pp.__version__)
pp.ParserElement.enable_left_recursion()

shows:

3.0.9
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
[<ipython-input-3-391db87ce479>](https://localhost:8080/#) in <cell line: 3>()
      1 import pyparsing as pp
      2 print(pp.__version__)
----> 3 pp.ParserElement.enable_left_recursion()

[/usr/local/lib/python3.9/dist-packages/pyparsing/core.py](https://localhost:8080/#) in enable_left_recursion(cache_size_limit, force)
   1021             ParserElement.disable_memoization()
   1022         elif ParserElement._packratEnabled:
-> 1023             raise RuntimeError("Packrat and Bounded Recursion are not compatible")
   1024         if cache_size_limit is None:
   1025             ParserElement.recursion_memos = _UnboundedMemo()

RuntimeError: Packrat and Bounded Recursion are not compatible

What could be wrong? Thanks.

[Hugues Hoppe]

I found the source of the problem.
When import matplotlib.pyplot is performed, it executes:

matplotlib/_mathtext.py:29: ParserElement.enablePackrat()

(It seems that the Python runtime within https://colab.research.google.com/ somehow pre-executes such a statement as well.)

So I cannot use both matplotlib.pyplot (or Google Colab) and ParserElement.enable_left_recursion() in the same Python environment.

It might be nice to somehow allow multiple pyparsing environments (with different settings for different libraries) within the same Python session?

[Paul McGuire]

I'm glad you were able to locate the issue. You can disable the packrat cacheing by calling disable_memoization after importing matplotlib, and then enabling left recursion.

[Hugues Hoppe]

pp.ParserElement.disable_memoization() did the trick; thanks!