List Comprehension: local variable referenced before assignment

Question

The following code gives me: local variable 'param' referenced before assignment

value_per_label = [(label, value) \ for label, value in zip(gui_names(param),values) \ for (param, values) in parameters]

What am I doing wrong?

parameters looks like this:

parameters = [("A", (1,3,5)), ("B", (2,3,4))]

and I wish to convert it to:

value_per_label = [("A_min", 1), ("A_current", 3), ("A_max", 5), ("B_min", 2), ("B_current", 3), ("BA_max", 4)]

@Anmol_uppal No its a function returning a tuple of "gui ids". The data being passed to me is in a wierd format so I'm converting it to something more useful. — Baz
– Baz, Commented Feb 6, 2015 at 8:33

no_name · Accepted Answer · 2015-02-06 08:42:04Z

Let's convert it into a for loop (List comprehensions are basically faster, more readable for loops):

value_per_label = [] for label, value in zip(gui_names(param), values): for (param, values) in parameters: value_per_label.append((label, value))

The error is pretty obvious now

Edit: To fix it, change the for loop to this:

 value_per_label = [(value, label) for (param, values) in parameters \ for (label, value) in zip(gui_names(param), values)]

I think this gives the same result, I didn't test it though.

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