* import_fixes: stub transformers.conversion_mapping so peft 0.19.x imports on transformers 4.x
patch_peft_weight_converter_compatibility currently opens with
try:
from peft.utils import transformers_weight_conversion as twc
except (ImportError, AttributeError):
return
which silently no-ops on (peft 0.19.x, transformers 4.57.x): peft's
transformers_weight_conversion module unconditionally imports two
transformers-v5 submodules at module top
from transformers.conversion_mapping import ...
from transformers.core_model_loading import ...
and neither submodule exists on transformers < 5. peft itself only USES
those submodules inside an is_transformers_ge_v5 branch, but the top of
file import still explodes with
ModuleNotFoundError: No module named 'transformers.conversion_mapping'
The bare except above swallows that, so the weight converter compat
wrap never gets installed, and any downstream code that later does
from peft.utils import transformers_weight_conversion crashes with the
same ModuleNotFoundError.
Fix: synthesise minimal stub modules for transformers.conversion_mapping
and transformers.core_model_loading, install them into sys.modules, and
re-import peft.utils.transformers_weight_conversion so the kwargs compat
wrap can succeed on top. The stubs expose exactly the symbols peft 0.19.x
pulls in at module top (Concatenate / ConversionOps are real subclassable
classes since peft subclasses them as PeftConcatenate / FlattenDims /
PermuteDims), so peft's own class creation succeeds. None of the stubbed
callables actually fire on the 4.x branch because peft's runtime
is_transformers_ge_v5 gate keeps them unreachable.
Gating contract (strict no-op outside the (peft 0.19.x, transformers 4.x)
combination):
* No-op if peft is not installed.
* No-op if peft.utils.transformers_weight_conversion already imports
clean (transformers v5+, or any peft fork off the v5 path).
* Strictly additive: only stubs submodules that are currently missing
from sys.modules / find_spec. We never overwrite the real
transformers.conversion_mapping / transformers.core_model_loading
on transformers v5+.
* Idempotent: sentinel attribute (__unsloth_stub__) on the stub modules
makes a second call return False, a third call return False, etc.
* Surfaces drift unchanged: if peft fails for some reason OTHER than
these two specific missing submodules, the original ImportError is
left for the caller's own try/except to take over.
Forwards / backwards compatibility:
* transformers 4.57.6 -> install stubs.
* transformers 5.x (real submodules) -> first-import probe succeeds,
return False, never touch sys.modules.
* TRL 0.22 / 0.27 / 1.x -- none of these import either submodule
directly; they reach the peft conversion module (if at all) through
peft.tuners.tuners_utils, behind peft's own is_transformers_ge_v5
gate. Stubs are therefore unreachable from TRL on a 4.x install,
and on a 5.x install the real submodules win the import race.
* peft 0.18 / 0.19 / 0.20 -- the symbols stubbed cover the union of
what peft pulls at module top across the 0.19.x line; older peft
that doesn't import the v5 submodules at all hits the cheap
first-import-probe exit and we never touch sys.modules.
Wired into unsloth/_gpu_init.py to run BEFORE
patch_peft_weight_converter_compatibility (otherwise that function's
bare except would still silently no-op). Mirrors the equivalent fix
shipped in unsloth-zoo (the zoo-side stub installs itself via
apply_import_fixes() at zoo import time, but a user can run
unsloth without the zoo fix on an older unsloth_zoo, so the unsloth
side needs to own its own copy of the workaround).
tests/conftest.py is updated to pre-apply this specific fix via the
standalone import-fixes module so the GPU-free drift detector test
(tests/test_import_fixes_drift.py::test_peft_transformers_weight_conversion_importable_and_signature)
sees the same patched state that a real ``import unsloth`` would.
The pattern mirrors unsloth-zoo's tests/conftest.py
_apply_zoo_import_fixes_for_tests helper, scoped to just the peft fix.
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