Question

What is the Python mechanism that makes it so that

[lambda: x for x in range(5)][2]()

is 4?

What is the usual trick for binding a copy of x to each lamba expression so that the above expression will equal 2?

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My final solution:

for template, model in zip(model_templates, model_classes):
    def create_known_parameters(known_parms):
        return lambda self: [getattr(self, p.name)
                             for p in known_parms]
    model.known_parameters = create_known_parameters(template.known_parms)

Answer 1

I usually use functools.partial:

[ partial(lambda x: x, x) for x in range(5) ]

Or, of course, you can do it yourself:

[ (lambda x: (lambda: x))(x) for x in range(5) ]