code: def from_variant_and_transcript(
              cls,
              variant,
              transcript,
              context_size):
          if not transcript.contains_start_codon:
              logger.info(
                  "Expected transcript %s for variant %s to have start codon",
                  transcript.name,
                  variant)
              return None
          if not transcript.contains_stop_codon:
              logger.info(
                  "Expected transcript %s for variant %s to have stop codon",
                  transcript.name,
                  variant)
              return None
          if not transcript.protein_sequence:
              logger.info(
                  "Expected transript %s for variant %s to have protein sequence",
                  transcript.name,
                  variant)
              return None
          sequence_key = ReferenceSequenceKey.from_variant_and_transcript(
              variant=variant,
              transcript=transcript,
              context_size=context_size)
          if sequence_key is None:
              logger.info(
                  "No sequence key for variant %s on transcript %s",
                  variant,
                  transcript.name)
              return None
          return cls.from_variant_and_transcript_and_sequence_key(
              variant=variant,
              transcript=transcript,
              sequence_key=sequence_key)