New in version 2.0.
Retain sequence elements at indices:
abjad> from abjad.tools import sequencetools
abjad> sequencetools.retain_sequence_elements_at_indices(range(20), [1, 16, 17, 18])
[1, 16, 17, 18]
Return sequence elements in the order they appear in sequence.
Ignore negative indices.
Return list.