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I was able to cobble my way through the C docs and write what I think is a reasonable attempt at a pure C dedent function (I forgot how fun -- albiet time consuming --- pointer logic can be).

To highlight some of the corner cases that need to be accounted for, this is the test case I'm using locally:

python -c "
import subprocess
# Use $ to note when a line will have all whitespace
lines = '''
         $

  $
    data = \"\"\"
    
    this data has newlines above and below  $
                            $

    \"\"\"
    if 1:         $
        print(123)$

    print(12345)
    print(repr(data))
'''.replace('$', '')
subprocess.run(['./python', '-c', lines])
"

I still haven't handled tabs, but I think my space logic is correct. I do need help vetting my C code and fixing the memory and security problems with it.

Delete all your wchar_t stuff. It is error-prone and unnecessary.

Delete all your _unicode_dedent. It is lengthy. Do utf_8_bytes_dedent is much more concise and simpler.

You should act fast since 3.12 release window will soon close. No new feature after May 8.
https://peps.python.org/pep-0693/

Can you give me write access to your branch?

@sunmy2019 I gave you access to my cpython fork.

I got one thought:

textwrap.dedent remove space and tabs.
https://docs.python.org/3/library/textwrap.html#textwrap.dedent

textwrap.dedent("""
 \t\t1
   2""")
'\n\t\t1\n  2'

It requires remembering the exact "space and tab prefix". Should we implement this?

It requires remembering the exact "space and tab prefix". Should we implement this?

Probably, but off the top of my head I'm not sure what the most elegant way to do it would be. I suppose instead of maintaining the tab and space counts, it would be sufficient to maintain the current shortest whitespace sequence, and then check how much of that sequence new lines match, shortening the sequence as necessary. I can give that a try.

On a different note, I'm sure that new features will want tests associated with them, but I'm not sure where the other "-c" tests live. Do you know where the best spot to put tests would be?

I got one thought:

textwrap.dedent remove space and tabs.

@Erotemic, take a look. I have implemented it with production quality at d336ac7.

Edit your #103998 (comment) to make it clear and concise, so that we can attract more reviewers.

On a different note, I'm sure that new features will want tests associated with them, but I'm not sure where the other "-c" tests live. Do you know where the best spot to put tests would be?

I guess Lib/test/test_cmd_line.py

We need someone with write access to review this.

@vstinner as the recent maintainer of this file.
@hauntsaninja