code: def _strip_column_name(col_name, keep_paren_contents=True):
      
      # start with input
      new_col_name = col_name
      # replace meaningful punctuation with text equivalents
      # surround each with whitespace to enforce consistent use of _
      punctuation_to_text = {
          '<=': 'le',
          '>=': 'ge',
          '=<': 'le',
          '=>': 'ge',
          '<': 'lt',
          '>': 'gt',
          '#': 'num'
      }
      for punctuation, punctuation_text in punctuation_to_text.items():
          new_col_name = new_col_name.replace(punctuation, punctuation_text)
  
      # remove contents within ()
      if not(keep_paren_contents):
          new_col_name = re.sub('\([^)]*\)', '', new_col_name)
  
      # replace remaining punctuation/whitespace with _
      punct_pattern = '[\W_]+'
      punct_replacement = '_'
      new_col_name = re.sub(punct_pattern, punct_replacement, new_col_name)
  
      # remove leading/trailing _ if it exists (if last char was punctuation)
      new_col_name = new_col_name.strip("_")
  
      # TODO: check for empty string
  
      # return lower-case version of column name
      return new_col_name.lower()
docs: Utility script applying several regexs to a string.
      Intended to be used by `strip_column_names`.
  
      This function will:
          1. replace informative punctuation components with text
          2. (optionally) remove text within parentheses
          3. replace remaining punctuation/whitespace with _
          4. strip leading/trailing punctuation/whitespace
  
      Parameters
      ----------
      col_name (str): input character string
      keep_paren_contents (logical):
          controls behavior of within-paren elements of text
           - if True, (the default) all text within parens retained
           - if False, text within parens will be removed from the field name
  
      Returns
      --------
      modified string for new field name
  
      Examples
      --------
      > print([_strip_column_name(col) for col in ['PD-L1','PD L1','PD L1_']])