Can't repeat negated pattern using \@!

Question

I have this text:

```python
x = 1
```

Basically markdown python cells. I would like to extract the content of the cell surrounding the cursor, if any.

As you may have guessed already, I am trying to build a jupyter workflow, I use jupytex and vim-slime for the console, and I would like to send cells to the console.

Currently I am struggling just matching a cell with regex:

/```python\(\(```\)\@!\)*```

This should match a string starting with ```python, then everything except triple quotes, then triple quotes, but it doesn't.

Strangely, this one(without the ending triple quotes:

/```python\(\(```\)\@!\)*

highlights ```python, but nothing more.

So what would be a regex to match a python cell? Bonus for a regex that matches the content of the cell under cursor!

Answer 1

This should match a string starting with ```python, then everything except triple quotes, then triple quotes, but it doesn't.

That's because the * multi does not repeat any character; it just repeats a negative lookahead, which doesn't add anything to the overall match. The regex engine can't reach the closing triple backticks.

/```python\(\(```\)\@!\)*```
            ^--------^
                ✘

Add a character inside:

/```python\(\(```\)\@!\_.\)*```
                      ^-^

Note that \_. can match any character, including a newline; contrary to . which can't match a newline. See :h /\_.

---

So what would be a regex to match a python cell? Bonus for a regex that matches the content of the cell under cursor!

Try this:

```python\n\%(\%(```\)\@!\_.\)*\%#\_.\{-}\n```\n
                               ├─┘   ├──┘
                               │     └ as few as possible
                               └ the cursor position must match here

See :h /\%#, and :h /\{-.

Answer 2

I don't understand those advanced regexes, but this one should do:

^```python\_$\_.\{-}\_^```$

To understand it, let :help ordinary_atom guide us:

• \_$ matches end-of-line.
• \_. matches any character, including end-of-lines.
• \_^ matches start-of-line.

And with :help non-greedy,

• \{-} is the same as * but uses the shortest match first algorithm. Remember that it applies only to the previous element, \_. in our case.

You may want to relax the regex a bit, maybe removing the ^ and $ anchoring.

Tested in this sample, the regex matches only the python cells.

This is Python:
```python
for i in range(10):
    print(i)
```
This is FORTRAN:
```fortran
DO I=1,10
    WRITE(*,*)I
ENDDO
```
This is Python again
```python
for i in range(10):
print('```')
```