Fix dependency specification in setup.py

[shaded-enmity]

The correct key name that is picked up by pip in setup.py is install_requires:
https://github.com/pazz/urwidtrees/blob/master/setup.py#L15

Trying to install urwidtrees without having urwid installed results in:

> $ pip install urwidtrees                                                                                    [±master ●]
Collecting urwidtrees
  Using cached urwidtrees-1.0.1.1.tar.gz
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-build-VGDG1V/urwidtrees/setup.py", line 4, in <module>
        import urwidtrees.version as v
      File "urwidtrees/__init__.py", line 6, in <module>
        from .decoration import DecoratedTree, CollapsibleTree
      File "urwidtrees/decoration.py", line 4, in <module>
        import urwid
    ImportError: No module named urwid

    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-VGDG1V/urwidtrees/

[pazz]

I think this could be fixed with an

install_requires=['urwid']

in the setup.py. I am not maintaining the pip version myself, but would accept a
PR for this.

[lucc]

I am not sure if this will solve it:

git clone https://github.com/pazz/urwidtrees
cd urwidtrees
virtualenv foo
source foo/bin/activate
sed -i 's/)$/install_requires=["urwid"])/' setup.py
pip install .

still gives the import error.

The question is rather: I think it would be better to either put the version definition somewhere else or remove all these imports from init. Then we can import the version during install without importing the complete package (which I hope is not used during install, just the version number).

[lucc]

After some tests I conclude that you should either hard code the version and other meta info into setup.py or not import everything into init.py . Becasue init will be loaded no matter which submodule of a package you import so the import error will persist.

[lucc]

This is also relevant to pazz/alot#886.