listtools.sign

abjad.tools.listtools.sign(l)

Return 1 when all elements in l are positive.

abjad> listtools.sign([1, 2, 3])
1

Return -1 when all elements in l are negative.

abjad> listtools.sign([-1, -2, -3])
-1

Return 0 when l is empty.

abjad> listtools.sign([ ])
0

Otherwise, return None.

abjad> listtools.sign([1, 2, -3]) is None
True

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