Hi Adrian, Thanks for the report. I was hoping to get a quick answer from https://github.com/FactoryBoy/factory_boy/issues/552 to push the new version of factory-boy without patching but I'll probably try to update the package and add the patch for python 3.7 that has been already merged so that the FTBS is fixed. I'll probably do that tomorrow if Brian is ok with it.
Thanks, Joseph