pip install lxml

to install mmcv-full requires the following command:

pip uninstall mmcv mmcv-full
git clone https://github.com/open-mmlab/mmcv.git
cd mmcv
MMCV_WITH_OPS=1 pip install -e .

the following error occurred while performing the last step:

command 'gcc' failed with exit status 4

so the solution:

1, check to see if disk space is sufficient

2.

pip install lxml