Simplifying a list comprehension

Question

How would I write the following more concisely?

    genres = ','.join([item for item in list((sheet.cell(n,18).value, 
                      sheet.cell(n,19).value, sheet.cell(n,20).value)) if item])

Answer 1

','.join(filter(None, (sheet.cell(n, i).value for i in (18, 19, 20))))

The (sheet.cell(n, i).value for i in (18, 19, 20)) is a generator expression replacing the list(…) part. You may replace the tuple (18, 19, 20) with a range or something else.

The filter(None, iterable) is equivalent to (x for x in iterable if x) . (In Python 2.x you may want to use itertools.ifilter instead.)

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Note also that, you can create a list using

[sheet.cell(n,18).value, sheet.cell(n,19).value, sheet.cell(n,20).value]

instead of the longer list((sheet.cell(n,18).value, …)) .

Answer 2

On two lines. Readability trumps conciseness.

Your list comprehension is also unnecessary, a genexp will do fine.

genre_values = (sheet.cell(n, i).value for i in xrange(18, 21))
genres = ", ".join(value for value in genre_cells if value)