code: def fastaWrite(fileHandleOrFile, name, seq, mode="w"):
      
      fileHandle = _getFileHandle(fileHandleOrFile, mode)
      valid_chars = {x for x in string.ascii_letters + "-"}
      try:
          assert any([isinstance(seq, unicode), isinstance(seq, str)])
      except AssertionError:
          raise RuntimeError("Sequence is not unicode or string")
      try:
          assert all(x in valid_chars for x in seq)
      except AssertionError:
          bad_chars = {x for x in seq if x not in valid_chars}
          raise RuntimeError("Invalid FASTA character(s) see in fasta sequence: {}".format(bad_chars))
      fileHandle.write(">%s\n" % name)
      chunkSize = 100
      for i in xrange(0, len(seq), chunkSize):
          fileHandle.write("%s\n" % seq[i:i+chunkSize])
      if isinstance(fileHandleOrFile, "".__class__):
          fileHandle.close()
docs: Writes out fasta file