code: def txtsubst(lines, variables, target_file=None, charset=None):
      
      if target_file:
          LOG.info("In process of generating file %r", target_file)
  
      if not charset:
          return [linesubst(line, variables) for line in lines]
  
      ret = []
      for line in lines:
          linesub = linesubst(line, variables)
          if isinstance(line, unicode):
              ret.append(linesub.encode(charset))
          else:
              ret.append(linesub)
      return ret
docs: Log that target_file is going to be generated, and calculate its
      content by applying the linesubst() transformation with the given
      variables to each given lines.