Make the gradient-accumulation rewrite emit group references

[vineethsaivs]

What breaks

patch_gradient_accumulation_fix rewrites training_step so accelerator.backward runs on the divided loss instead of the full one. The regex is raw. The replacement is not:

"else:\n"
"\2if num_items_in_batch is None:\n"
"\3loss = loss / self.args.gradient_accumulation_steps\n"
"\1self.accelerator.backward(loss, **kwargs)",

"\1", "\2" and "\3" are octal escapes. Python turns them into 0x01, 0x02 and 0x03 long before re.sub gets a chance to read them as group references, so the three captured indents come back as control characters:

'else:\n\x02if num_items_in_batch is None:\n\x03loss = loss / self.args.gradient_accumulation_steps\n\x01self.accelerator.backward(loss, **kwargs)'

The exec(function, globals()) two lines below then raises SyntaxError: unexpected indent rather than installing the patched training_step.

What changed

A raw template with \g<1>, \g<2>, \g<3>. The rewrite now produces what it was written to produce:

    else:
        if num_items_in_batch is None:
            loss = loss / self.args.gradient_accumulation_steps
        self.accelerator.backward(loss, **kwargs)
    return loss.detach()

How live is it

Not live. The shape this matches is what training_step looked like before huggingface/transformers#35808 reordered the two. I checked the whole pinned range in pyproject.toml (transformers>=4.51.3,<=5.5.0):

version	pattern matches
4.51.3 (minimum pin)	no
4.56.0	no
5.5.0 (maximum pin)	no

So today the branch is a silent no-op, and this is a landmine rather than a crash anyone is hitting. Deleting the block is a fair call instead and I am happy to send that version if you prefer it. I did not assume it, because the other three replacements in the same function are also inert on these versions and I did not want to decide that for you.

Tests

tests/test_gradient_accumulation_rewrite.py reads the pattern and the replacement out of _utils.py with ast and runs them against the old training_step shape, since _utils.py cannot be imported without an accelerator.

• the rewrite moves backward below the division
• the result carries no control characters, parses, and keeps backward one indent level outside the if

2 passed in 0.20s

The second fails on main:

assert not any(character in rewritten for character in "\x01\x02\x03")
E  assert not True

[danielhanchen]

Confirmed the replacement in unsloth/models/_utils.py still uses plain backslash-digit strings, so the captured indents come back as control bytes if that pattern ever matches again. Will get this reviewed, and I may take you up on the delete-the-block variant instead.