ENH add --negate flag to pygrep

[MarcoGorelli]

xref this comment on StackOverflow: https://stackoverflow.com/a/64344519/9988333

A PR may be considered if you can demonstrate a real use case for it

A use-case comes from PyMC3, where there is a pre-commit hook to check that all notebooks have a watermark. Currently, this is done by defining

- repo: local
  hooks:
    - id: watermark
      name: Check notebooks have watermark
      types: [jupyter]
      entry: python scripts/check_watermark.py
      language: python

in https://github.com/pymc-devs/pymc3/blob/master/.pre-commit-config.yaml, and then

"""
Check that given Jupyter notebooks all contain a final watermark cell to facilite reproducibility.
This is intended to be used as a pre-commit hook, see `.pre-commit-config.yaml`.
You can run it manually with `pre-commit run watermark --all`.
"""

import argparse
from pathlib import Path
import re

if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("filenames", nargs="*")
    args = parser.parse_args()
    for file_ in args.filenames:
        assert (
            re.search(
                r"%load_ext watermark.*%watermark -n -u -v -iv -w",
                Path(file_).read_text(),
                flags=re.DOTALL,
            )
            is not None
        ), (
            f"Watermark not found in {file_} - please see the PyMC3 Jupyter Notebook Style guide:\n"
            "https://github.com/pymc-devs/pymc3/wiki/PyMC's-Jupyter-Notebook-Style"
        )

in https://github.com/pymc-devs/pymc3/blob/master/scripts/check_watermark.py .

---

I think the output should be a file which does not contain the pattern...I'll work on this tomorrow

[MarcoGorelli]

Marking as ready for review as I'd like to think this is enough to tell whether it's the right direction / whether the feature would be welcome. Thanks for the 'don't put logic in tests' link!

[asottile]

this can be return 0

and then below you can

else:
    output.write_line(filename)
    return 1

[MarcoGorelli]

Yes, much simpler, thanks!

Though here there wouldn't be an else, would there? It's necessary to check through all the lines before deciding to return 1

[asottile]

I mean for: ... else: ...

[MarcoGorelli]

Ah, I see, thanks! I see you have a video about this too, will watch now https://youtu.be/8P7lXLXR_3c

[asottile]

this should be outside the loop, otherwise you're doing this work every iteration instead of just once

[asottile]

[MarcoGorelli]

Thank you so much for the mentorship you provided me here, I really appreciate it, it's very kind of you!