Python package seems to ignore my requirements
Question: I created my first package. When I try to install it with pip in a newly
created virtualenv I get an error indicating that libs cannot be imported, yet
they are added to the `install_requires` field in `setup.py`. If I do it
outside a vierualenv, all is ok. My setup.py is here:
<https://github.com/tdi/pyPEPA/blob/dev/setup.py>

To reproduce the error:

    
    
    mkvirtualenv something -p /usr/bin/python3
    workon something
    pip install pypepa
    

.

    
    
    Downloading/unpacking pypepa
     Running setup.py egg_info for package pypepa
     Traceback (most recent call last):
      File "<string>", line 16, in <module>
      File "/home/tdi/.virtualenvs/koza/build/pypepa/setup.py", line 3, in <module>
        import pypepa
      File "./pypepa/__init__.py", line 6, in <module>
        from pypepa.pepa_model import PEPAModel
      File "./pypepa/pepa_model.py", line 6, in <module>
        from pypepa.parsing.parser import PEPAParser
      File "./pypepa/parsing/parser.py", line 5, in <module>
        from pyparsing import Word, Literal, alphas, alphanums, nums, Combine, Optional, ZeroOrMore, Forward, restOfLine
    ImportError: No module named 'pyparsing'
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
    File "<string>", line 16, in <module>
     File "/home/tdi/.virtualenvs/koza/build/pypepa/setup.py", line 3, in <module>
    import pypepa
    File "./pypepa/__init__.py", line 6, in <module>
    from pypepa.pepa_model import PEPAModel
     File "./pypepa/pepa_model.py", line 6, in <module>
    from pypepa.parsing.parser import PEPAParser
     File "./pypepa/parsing/parser.py", line 5, in <module>
      from pyparsing import Word, Literal, alphas, alphanums, nums, Combine, Optional, ZeroOrMore, Forward, restOfLine
     ImportError: No module named 'pyparsing'
     ----------------------------------------
     Command python setup.py egg_info failed with error code 1 in      /home/tdi/.virtualenvs/koza/build/pypepa
     Storing complete log in /home/tdi/.pip/pip.log
    


Answer: Your setup script imports pypepa which imports pypepa.pepa_model which imports
pyparsing, but pyparsing is not installed yet (we haven’t even finished
running the setup script to know what the dependencies are). The solution is
to repeat the version number in pypepa and setup.py (so you can remove the
import), or not import PEPAModel in __init__.py.

