Provide a more helpful error on pip install.

[danielballan]

A somewhat silly first PR, but it might help someone.

I like and always use the pattern of parsing requirements.txt to populate the install_requires parameter in setup.py. But an annoying restriction to keep in mind is that while

pip install -r requirements.txt

works with git+https://... specifications, install_requires only accepts proper packages on a packaging index (e.g. PyPI). There is not a good workaround for this as far as I know. All you can do is provide a more helpful error message.

Before:

$ pip install -e .
Obtaining file:///home/dallan/Repos/bnl/splash-server
    ERROR: Command errored out with exit status 1:
     command: /home/dallan/miniconda3/envs/py38/bin/python -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/home/dallan/Repos/bnl/splash-server/setup.py'"'"'; __file__='"'"'/home/dallan/Repos/bnl/splash-server/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-pip-egg-info-pxhdmmpn
         cwd: /home/dallan/Repos/bnl/splash-server/
    Complete output (1 lines):
    error in splash-server setup command: 'install_requires' must be a string or list of strings containing valid project/version requirement specifiers; Parse error at "'+https:/'": Expected stringEnd
    ----------------------------------------

After:

$ pip install -e .
Obtaining file:///home/dallan/Repos/bnl/splash-server
    ERROR: Command errored out with exit status 1:
     command: /home/dallan/miniconda3/envs/py38/bin/python -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/home/dallan/Repos/bnl/splash-server/setup.py'"'"'; __file__='"'"'/home/dallan/Repos/bnl/splash-server/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-pip-egg-info-y7mgc4v3
         cwd: /home/dallan/Repos/bnl/splash-server/
    Complete output (6 lines):
    
    
    You must manually install databroker_fitshandler:
    pip install git+git://github.com/als-computing/datahandler_fits@master#egg=databroker-fitshandler
    
    
    ----------------------------------------
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.

[dylanmcreynolds]

Thanks for this @danielballan