Add format or automatic format parsing to dot.render()

[geyang]

Hi @xflr6 ,

Thanks for this library!

I would like to request adding either

1. a new attribute format to the dot.render() function

or / and

2. make the dot.render function automatically parse the file format from the render path.

I can submit a pull request if needed, just want to discuss this first.

The pain-point at the moment is that to save the graph, I need to either

g = Graph(format="svg")
... # Losts of code

g.render(path="figures/this_particular_figure")

or do

g.format = "svg"
g.render(path="....")

and none of these is very appealing.

Thanks!
Ge

[xflr6]

Thanks, glad if it is somewhat useful.
Not completely sure this is about the right thing though, as the .render()-method has no path argument:

>>> from graphviz import Graph
>>> g = Graph(format="svg")
>>> g.node('spam')
>>> g.render(path='spam')
Traceback (most recent call last):
  File "<pyshell#12>", line 1, in <module>
    g.render(path='spam')
TypeError: render() got an unexpected keyword argument 'path'

The method does have filename and directory arguments. However, the former is for the name of the source (DOT, text) file. The actual rendering then does dot -Tsvg -O Graph.gv which automatically appends the right file extension to the name (in this case, the rendered file would be Graph.gv.svg):

 -O          - Automatically generate an output filename based on the input file
name with a .'format' appended. (Causes all -ofile options to be ignored.)

In other words, this follows the idea from the Graphviz commands to specify the format to infer the file extension from instead of the other way around (which AFAIU is what you want to propose, right?).
Note that this is why the .render()-method returns the path to the rendered file.

Note that by default filename is inferred from name, so maybe you want to try:

>>> import graphviz
>>> g = graphviz.Graph('fig1', directory='figures', format='svg')
>>> g.node('spam')
>>> g.render()
'figures/fig1.gv.svg'