Update requirements.txt

[gstein]

The "graphviz" Python module is required. Clarify that within the requirements.

(the graphviz/dot commands are needed at the OS level, but that can't be fixed here)

[17o2]

What's the difference between declaring this in requirements.txt as opposed to setup.py (see linked line)?

Since I'm not familiar with creating Python packages myself, maybe @n42 can be of help as the author of the refactoring?

If we add it to requirements.txt, pyyaml should also be listed.

[gstein]

That's quite a fair question, and I see that pyyaml is in setup.py (which could/should also be moved!) ... by moving it to requirements.txt, tools can consume the set of needed modules (whereas, they cannot discover the set from setup.py).

For example:
$ pip install -r requirements.txt

[gstein]

(honestly, I didn't even stop to look into setup.py ... I always go to requirements.txt first :p )

[n42]

A difference is iirc that requirements.txt is mainly useful in that it's easily human-readable and can be used for explicitly installing only the dependencies, which might be useful for using packages without installing them first. Pip/setuptools will use what's listed in setup.py as required dependencies and install them automatically if you use that to install the package.

[n42]

It doesn't hurt anything to use both methods, but I'd suggest adding the pyyaml dep in the reqs file as well if you want to use that.

[17o2]

So it's fine to have in both places? I'll just add two lines into requirements.txt file and leave setup.py untouched. Thanks.

[n42]

Yeah, perfectly fine. There should be a way to have setup.py parse requirements.txt instead of having multiple places to define them as well, but I seem to recall something about pip version fuckery wrt that. I'll look into it when I'm at an actual computer.

[17o2]

Cheers! I'll wait until then, I don't see this as a super urgent issue.

[gstein]

Agree: not urgent. Per discussion, I've included pyyaml into the PR.

[17o2]

Merged and closed for now. If we want to update setup.py to parse requirements.txt in the future, we can open a new PR. In the meantime, if more requirements appear, they'll be added to both files.