code: def to_int(x, index=False):
      
      _x = x.index if index else x
      cols = list(map(int, _x))
      error = _x[cols != _x]
      if not error.empty:
          raise ValueError('invalid values `{}`'.format(list(error)))
      if index:
          x.index = cols
          return x
      else:
          return _x
docs: Formatting series or timeseries columns to int and checking validity.
      If `index=False`, the function works on the `pd.Series x`; else,
      the function casts the index of `x` to int and returns x with a new index.