docs: def _cellrepr(value, allow_formulas):
      """
      Get a string representation of dataframe value.
  
      :param :value: the value to represent
      :param :allow_formulas: if True, allow values starting with '='
              to be interpreted as formulas; otherwise, escape
              them with an apostrophe to avoid formula interpretation.
      """
      if pd.isnull(value) is True:
          return ""
      if isinstance(value, float):
          value = repr(value)
      else:
          value = str(value)
      if (not allow_formulas) and value.startswith('='):
          value = "'%s" % value
      return value