code: def validate_col(self, itemsize=None):
          
  
          # validate this column for string truncation (or reset to the max size)
          if _ensure_decoded(self.kind) == 'string':
              c = self.col
              if c is not None:
                  if itemsize is None:
                      itemsize = self.itemsize
                  if c.itemsize < itemsize:
                      raise ValueError(
                          "Trying to store a string with len [{itemsize}] in "
                          "[{cname}] column but\nthis column has a limit of "
                          "[{c_itemsize}]!\nConsider using min_itemsize to "
                          "preset the sizes on these columns".format(
                              itemsize=itemsize, cname=self.cname,
                              c_itemsize=c.itemsize))
                  return c.itemsize
  
          return None
docs: validate this column: return the compared against itemsize