Implement svg output in notebooks #29

[benabel]

This implementation use a simple algorithm in which the layout used is
based on a perfect tree of same height in which all leaves would be
regularly spaced.

This approach is ok for little trees to about 4 levels but for larger trees
with holes a better approach would be to implement the Reingold &
Tilford’s algorithm.

[benabel]

@joowani Currently the 2.7 and 3.5 tests fails because the code is using f-strings that were added in python 3.5.

https://docs.python.org/3/reference/lexical_analysis.html#f-strings

Do you to maintain compatibility with these python versions even if they have reached their end-of-life:

https://devguide.python.org/devcycle/#end-of-life-branches

[joowani]

Hi @benabel,

Thanks for the PR! Yes I am planning to drop support for those two, and I'm also planning to switch over to github actions etc as well. I'll keep this open and re-evaluate after.

[joowani]

Instead of implementing this method from scratch, I've decided to use python-graphviz instead (it has many more features including Jupyter notebook support) in version 6.0.0. Please see the documentation for more details.

[benabel]

@joowani using phython-graphviz adds dependecies on python side and on system side with the graphviz binary. For users like teachers that don't have any rights on a machine this feature will be unavailable. You could use a try except and fallback to my implementation if graphviz isn't available on the system.

[joowani]

Awesome PR!

[joowani]

This can just be str now.

[joowani]

Please change to Generate the coordinates used for rendering the nodes and edges.

[joowani]

This can be removed.

[joowani]

Since you are importing this outside of the module, should be renamed to get_coords.

[benabel]

This is only used on layout module and test.

[joowani]

Hi @benabel,

I like your idea. I've reopened the PR and left some comments. Could you please address them and rebase? Thanks again for your contribution.

[benabel]

@joowani I tried to amend the code using your suggestions, however I can't pass the doctests.

[benabel]

@joowani In fact the doctests fails due to the graphviz method. My changes seems ok, I added typings and unit tests passes.

graphviz doesn't seem to be installed in build.yaml.

2 Errors in task Run Sphinx doctest:

Failed example:
    graph.body              # Get the DOT body
Expected nothing
Got:
    ['\t140536390881360 [label="<l>|<v> 4|<r>"]', '\t140536390881360:l -> 140536390659728:v', '\t140536390881360:r -> 140536390660048:v', '\t140536390659728 [label="<l>|<v> 13|<r>"]', '\t140536390659728:l -> 140536390659472:v', '\t140536390659728:r -> 140536390657424:v', '\t140536390660048 [label="<l>|<v> 1|<r>"]', '\t140536390660048:l -> 140536390573584:...

graphviz.backend.ExecutableNotFound: failed to execute ['dot', '-Kdot', '-Tpdf', '-O', 'Digraph.gv'], make sure the Graphviz executables are on your systems' PATH

[joowani]

Hi @benabel,

No worries, I can take care of the clean up. Thanks again for your contribution! This is very useful.

[benabel]

You're welcome @joowani. Thanks for sharing this package.