OSError but disk space does not seem to be full

My disk quota seems to be only half full (Files tab) but getting following error when doing a pip install -r requirements.txt

OSError: [Errno 122] Disk quota exceeded

It's possible that your requirements would fill the disk quota; when you do a pip install, it tries to install everything, but it it gets an error then it will clear down stuff that it's already done, which will free up the disk space again.