René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Unexpected(?) behaviour in `Graph.apply`","articleBody":"I ran into an issue today while attempting repeated evaluations of a graph. My rough usage pattern looks like this:\r\n\r\n```python\r\ncontext = {'a': 1, 'b': 2}\r\nfor df in frames:\r\n\tout = graph(outputs, context=context, frame=df)\r\n```\r\n\r\nWhich worked fine for the first call but fails with the following error on the second call:\r\n\r\n```python\r\nValueError: duplicate value for operation '\u003cpf.placeholder 'first_input'\u003e'\r\n```\r\n\r\nAfter some digging, I noticed that the `Graph.normalize_context` method modifies the `context` in-place. It is not mentioned in the documentation, and given the semantics of a `Graph.apply` this does not seem like an expected (or desired?) side-effect.\r\n\r\nIs this something that should be updated in the documentation? Should `Graph.normalize_context` be modified to copy the context and not modify it in-place? Or is there a better pattern I should be using if I need to repeatedly call the graph object with some constant context and a handful of varying placeholders? (It probably wouldn't hurt to update the documentation with that pattern if there is one).","author":{"url":"https://github.com/easyas314159","@type":"Person","name":"easyas314159"},"datePublished":"2019-10-18T08:03:47.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/43/pythonflow/issues/43"}