PEP 479 breaks functions that are based on generators in Python 3.7

[nicolastorzec]

Hi,

PEP 479 changes the way StopIteration is handled within generators. Pre-3.7, generators used to exit gracefully, but in 3.7 they result in a RuntimeError.

As a result, functions like successors() or subgraph() are no longer working and raise a RuntimeError with 3.7.

Trace below:

---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
~/Workspace/VirtualEnv/py370/lib/python3.7/site-packages/pygraphviz/agraph.py in successors_iter(self, n)
    809             eh = gv.agnxtout(self.handle, eh)
--> 810         raise StopIteration
    811 

StopIteration: 

The above exception was the direct cause of the following exception:

RuntimeError                              Traceback (most recent call last)
<ipython-input-14-39154a6704d5> in <module>()
----> 1 Image(gpt.draw(root='ROOT', max_depth=1), retina=True)

~/Workspace/gptlib.py in draw(self, root, max_depth, format, filename)
    203                     yield from get_subtree_nodes(s, d-1)
    204 
--> 205         sg = self.__gpt_graph.subgraph([root] + [n for n in get_subtree_nodes(root, max_depth)])
    206 
    207         sg.layout(prog='dot')

~/Workspace/gptlib.py in <listcomp>(.0)
    203                     yield from get_subtree_nodes(s, d-1)
    204 
--> 205         sg = self.__gpt_graph.subgraph([root] + [n for n in get_subtree_nodes(root, max_depth)])
    206 
    207         sg.layout(prog='dot')

~/Workspace/ProductKG/GoogleProductTaxonomy/gptlib.py in get_subtree_nodes(n, d)
    199 
    200             if d > 0:
--> 201                 for s in self.__gpt_graph.successors(n):
    202                     yield s
    203                     yield from get_subtree_nodes(s, d-1)

~/Workspace/VirtualEnv/py370/lib/python3.7/site-packages/pygraphviz/agraph.py in successors(self, n)
    814     def successors(self, n):
    815         """Return list of successor nodes of n."""
--> 816         return list(self.successors_iter(n))
    817 
    818 

RuntimeError: generator raised StopIteration

[dschult]

I think these are fixed in #164. We are preparing to make a release with the updates.

[nicolastorzec]

I git cloned and installed the upcoming release (i.e. pygraphviz-1.5.dev0-py3.7.egg-inf), and it indeed fixed the issues I had with subgraphs(), successors(), and other generator functions.

Thanks @dschult.