Cell-var-from-loop warning from Pylint

For the following code:

    for sort_key, order in query_data['sort']:
        results.sort(key=lambda k: get_from_dot_path(k, sort_key),
                     reverse=(order == -1))

Pylint reported an error:

Cell variable sort_key defined in loop (cell-var-from-loop)

Could anyone give a hint what is happening here? From pylint source code the description is:

A variable used in a closure is defined in a loop. This will result in all closures using the same value for the closed-over variable.

But I do not have a clue what it means. Could anyone give an example of the problem?

The name sort_key in the body of the lambda will be looked up when the function is actually called, so it will see what ever value sort_key had most recently. Since you are calling sort immediately, the value of sort_key will not change before the resulting function object is used, so you can safely ignore the warning. To silence it, you can make sort_key the default value of a parameter to the lambda:

    results.sort(key=lambda k, sk=sort_key: get_from_dot_path(k, sk),
                     reverse=(order == -1))

From: stackoverflow.com/q/25314547

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