Get all unique sequences from reads spanning a variant locus. This will
    include partial sequences due to reads starting in the middle of the
    sequence around around a variant.

def initial_variant_sequences_from_reads(
        variant_reads,
        max_nucleotides_before_variant=None,
        max_nucleotides_after_variant=None):
    """
    Get all unique sequences from reads spanning a variant locus. This will
    include partial sequences due to reads starting in the middle of the
    sequence around around a variant.
    """
    unique_sequence_groups = group_unique_sequences(
        variant_reads,
        max_prefix_size=max_nucleotides_before_variant,
        max_suffix_size=max_nucleotides_after_variant)

    return [
        VariantSequence(
            prefix=prefix,
            alt=alt,
            suffix=suffix,
            reads=reads)
        for ((prefix, alt, suffix), reads)
        in unique_sequence_groups.items()
    ]