code: def edit_distance_filter(source_target_input, max_equal_to_diff_ratio=0):
    
    thrown_out_count = 0
    source_target_output = []
  
    if not max_equal_to_diff_ratio:
      return source_target_input, thrown_out_count
  
    for src_tgt in source_target_input:
      opcodes = fast_match_sequences(*src_tgt)
      diff_char_count = 0
      equal_char_count = 0
      for tag, i1, i2, j1, j2 in opcodes:
        if tag == "diff":
          # max() prevents double-counting substitutions.
          diff_char_count += max(i2 - i1, j2 - j1)
        else:
          equal_char_count += i2 - i1
      if diff_char_count <= max_equal_to_diff_ratio * equal_char_count:
        source_target_output.append(src_tgt)
      else:
        thrown_out_count += 1
    return source_target_output, thrown_out_count
docs: Filter out examples that exceed max_edit_ratio between source and target.
  
    Args:
      source_target_input:     a list of [source, target] pairs
      max_equal_to_diff_ratio: cutoff for ratio of equal chars / diff chars
        between source and target
  
    Returns:
      source_target_output:    filtered subset of [source, target] input pairs
      thrown_out_count:        number of examples filtered out