code: def trim_variant_fields(location, ref, alt):
      
      if len(alt) > 0 and ref.startswith(alt):
          # if alt is a prefix of the ref sequence then we actually have a
          # deletion like:
          #   g.10 GTT > GT
          # which can be trimmed to
          #   g.12 'T'>''
          ref = ref[len(alt):]
          location += len(alt)
          alt = ""
      if len(ref) > 0 and alt.startswith(ref):
          # if ref sequence is a prefix of the alt sequence then we actually have
          # an insertion like:
          #   g.10 GT>GTT
          # which can be trimmed to
          #   g.11 ''>'T'
          # Note that we are selecting the position *before* the insertion
          # (as an arbitrary convention)
          alt = alt[len(ref):]
          location += len(ref) - 1
          ref = ""
      return location, ref, alt
docs: Trims common prefixes from the ref and alt sequences
  
      Parameters
      ----------
      location : int
          Position (starting from 1) on some chromosome
  
      ref : str
          Reference nucleotides
  
      alt : str
          Alternate (mutant) nucleotide
  
      Returns adjusted triplet (location, ref, alt)