Inherit render properties

[BMaxV]

Hi,

this is for #114 .

There are two things probably still have to be done:

I don't know what good non default values would be for 'encoding' and 'engine' for the test function.

There is a check in https://github.com/xflr6/graphviz/blob/master/graphviz/dot.py#L100 that subgraphs can't be strict, so it does not make sense to inherit that one.

[codecov-io]

Codecov Report

Merging #116 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #116   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            7         7           
  Lines          504       504           
=========================================
  Hits           504       504           

Impacted Files	Coverage Δ
graphviz/dot.py	100.00% <ø> (ø)
graphviz/backend.py	100.00% <0.00%> (ø)

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[xflr6]

This is handled by the super()-call in line 61 above:

graphviz/graphviz/files.py

Line 103 in 0c503a3

self.encoding = encoding

[xflr6]

Thanks for working on this.

I don't know what good non default values would be for 'encoding' and 'engine' for the test function.

How about 'ascii', and 'neato'?

There is a check in https://github.com/xflr6/graphviz/blob/master/graphviz/dot.py#L100 that subgraphs can't be strict, so it does not make sense to inherit that one.

graphviz/graphviz/dot.py

Lines 98 to 100 in 0c503a3

	if subgraph:
	if self.strict:
	raise ValueError('subgraphs cannot be strict')

+1. We should add a note to the .subgraph()-method that instances created with the context manager are always strict=None because the parent's value is used when rendering the parent graph (there is no way for the subgraph to override). This means if we render the subgraph in the context manager it is bool(strict) == False. If user's would really want to render the subgraph as strict while rendering the whole graph non-strict they could do like this.

(...)
with d.subgraph(name='child') as s:
    s.strict = True
    s.render('child.gv')
    s.strict = None  # any falsy value

I think we should add a functional test for the use case of doing render() on a subgraph within the context-manager, i.e. use tmpdir and assert on the rendered files. Not yet shure where to put it exactly.

Another thing would be to extend the the docstring and maybe also the documentation section and to write a short summary of the behavioural difference for the CHANGES.txt. Tell me if/when you prefer me to take over, then we can probably merge what you have.

[BMaxV]

I think this should be it. I didn't touch CHANGES.txt yet , that would still need to be done. It inherits the format now and that was the main thing I wanted, so I think you can take over now?

[xflr6]

Thanks. Still need a functional test, implement strict=None, more informative documentation and a proper note in the docstring, let me take if from here then.

[xflr6]

See adaptations in 4a20d2e