NodeList render overhead with huge templates

[Michal Čihař]

While debugging rendering of some huge templates, I've noticed that the rendering is slower and needs more memory than necessary because of:

    def render(self, context):
        return SafeString("".join([node.render_annotated(context) for node in self]))

which unnecessarily builds a list and then passes it to join, which could directly consume an iterable.

I will prepare a pull request with a fix.

[Mariusz Felisiak]

There is nothing to fix here. A list comprehension is preferable here as str.join() converts to list internally anyway. It is better performance to provide a list up front.

• ​https://stackoverflow.com/questions/9060653/list-comprehension-without-in-python/9061024#9061024
• ​https://github.com/adamchainz/flake8-comprehensions/issues/156