ModuleNotFoundError: No module named 'mmcv._ext'

[mbspng]

This is now part of the setup script of a project of mine:

    echo "Hacking MMDetection and MMDetection3D packages..."
    # Why? Because docs (https://mmcv.readthedocs.io/en/latest/get_started/installation.html) say
    #
    #   `pip install mmcv==2.2.0 -f https://download.openmmlab.com/mmcv/dist/cu121/torch2.4/index.html`
    #
    # (we used `uv add` of course) to match the other dependencies pinned in this repo.
    #
    # But then you end up with
    #
    #    `AssertionError: MMCV==2.2.0 is used but incompatible. Please install mmcv>=2.0.0rc4, <2.2.0`.
    #
    # Right, makes sense, eh?!
    #
    # And when installing 2.1.0, you get
    #
    #   `ModuleNotFoundError: No module named 'mmcv._ext'`.
    #
    # But when first installing 2.1.0, and then installing 2.2.0, and THEN hacking the `__init__.py` files, it works.
    # So, here we are.
    uv add mmcv==2.1.0 -f https://download.openmmlab.com/mmcv/dist/cu121/torch2.4/index.html
    uv add mmcv==2.2.0 -f https://download.openmmlab.com/mmcv/dist/cu121/torch2.4/index.html
    cp src/mmdet_init.py .venv/lib/python3.10/site-packages/mmdet/__init__.py
    cp src/mmdet3d_init.py .venv/lib/python3.10/site-packages/mmdet3d/__init__.py
    uv sync --all-extras

    echo "Setup complete."

-> % cat src/mmdet3d_init.py                  
# Copyright (c) OpenMMLab. All rights reserved.
import mmcv
import mmdet
import mmengine
from mmengine.utils import digit_version

from .version import __version__, version_info

mmcv_minimum_version = '2.0.0rc4'
mmcv_maximum_version = '2.2.0'
mmcv_version = digit_version(mmcv.__version__)

mmengine_minimum_version = '0.8.0'
mmengine_maximum_version = '1.0.0'
mmengine_version = digit_version(mmengine.__version__)

mmdet_minimum_version = '3.0.0rc5'
mmdet_maximum_version = '3.4.0'
mmdet_version = digit_version(mmdet.__version__)

# assert (mmcv_version >= digit_version(mmcv_minimum_version)
#         and mmcv_version < digit_version(mmcv_maximum_version)), \
#     f'MMCV=={mmcv.__version__} is used but incompatible. ' \
#     f'Please install mmcv>={mmcv_minimum_version}, <{mmcv_maximum_version}.'
#
# assert (mmengine_version >= digit_version(mmengine_minimum_version)
#         and mmengine_version < digit_version(mmengine_maximum_version)), \
#     f'MMEngine=={mmengine.__version__} is used but incompatible. ' \
#     f'Please install mmengine>={mmengine_minimum_version}, ' \
#     f'<{mmengine_maximum_version}.'
#
# assert (mmdet_version >= digit_version(mmdet_minimum_version)
#         and mmdet_version < digit_version(mmdet_maximum_version)), \
#     f'MMDET=={mmdet.__version__} is used but incompatible. ' \
#     f'Please install mmdet>={mmdet_minimum_version}, ' \
#     f'<{mmdet_maximum_version}.'

__all__ = ['__version__', 'version_info', 'digit_version']

-> % cat src/mmdet_init.py 
# Copyright (c) OpenMMLab. All rights reserved.
import mmcv
import mmengine
from mmengine.utils import digit_version

from .version import __version__, version_info

mmcv_minimum_version = '2.0.0rc4'
mmcv_maximum_version = '2.2.0'
mmcv_version = digit_version(mmcv.__version__)

mmengine_minimum_version = '0.7.1'
mmengine_maximum_version = '1.0.0'
mmengine_version = digit_version(mmengine.__version__)

# assert (mmcv_version >= digit_version(mmcv_minimum_version)
#         and mmcv_version < digit_version(mmcv_maximum_version)), \
#     f'MMCV=={mmcv.__version__} is used but incompatible. ' \
#     f'Please install mmcv>={mmcv_minimum_version}, <{mmcv_maximum_version}.'
#
# assert (mmengine_version >= digit_version(mmengine_minimum_version)
#         and mmengine_version < digit_version(mmengine_maximum_version)), \
#     f'MMEngine=={mmengine.__version__} is used but incompatible. ' \
#     f'Please install mmengine>={mmengine_minimum_version}, ' \
#     f'<{mmengine_maximum_version}.'

__all__ = ['__version__', 'version_info', 'digit_version']

├── mmdet v3.3.0 (extra: openmmlab)
├── mmdet3d v1.4.0 (extra: openmmlab)
├── torch v2.4.1 (extra: openmmlab)
├── torchaudio v2.4.1 (extra: openmmlab)
└── torchvision v0.19.1 (extra: openmmlab)

python 3.10.13

I think that speaks for itself.

[NicolasGonzalezF]

Same issue here , tried to install directly mmcv 2.2.0 , fails building the wheel, 2.0.4, says that it couldt find mmcv , im so confused because the google colab book is quite outdated at this point and for some is the only way to compile faster

[henryrobbins]

I managed to resolve the mmcv._ext issue when running the test installation script: python demo/image_demo.py demo/demo.jpg rtmdet_tiny_8xb32-300e_coco.py --weights rtmdet_tiny_8xb32-300e_coco_20220902_112414-78e30dcc.pth --device cpu!

I have an M3 Pro and a Python 3.11 miniconda installation. I created a virtual environment with python -m venv venv. Then, I installed the following packages:

pip install torch==2.1.2
pip install torchvision==0.16.2
pip install numpy==1.26.4
pip install openmim
mim install mmengine
mim install "mmcv==2.1.0"
mim install mmdet

I found it's important to use mim and not pip when installing the openmmlab packages.