You might have different confliciting versions installed with pip and pip3.
Try this, it should remove all versions of op1repacker on your system:
pip uninstall op1repacker
pip3 uninstall op1repacker
sudo pip uninstall op1repacker
sudo pip3 uninstall op1repacker
Then reinstall it with pip3 and check version:
pip3 install op1repacker
op1repacker --version