How to use the fitsio.util.isinteger function in fitsio

def __init__(self, fitshdu, columns):
        """
        Input is the FITS instance and a list of column names.
        """

        self.columns = columns
        if isstring(columns) or isinteger(columns):
            # this is to check if it exists
            self.colnums = [fitshdu._extract_colnum(columns)]

            self.is_scalar = True
            self.columns_list = [columns]
        else:
            # this is to check if it exists
            self.colnums = fitshdu._extract_colnums(columns)

            self.is_scalar = False
            self.columns_list = columns

        self.fitshdu = fitshdu

def _extract_colnum(self, col):
        """
        Get the column number for the input column
        """
        if isinteger(col):
            colnum = col

            if (colnum < 0) or (colnum > (self._ncol-1)):
                raise ValueError(
                    "column number should be in [0,%d]" % (0, self._ncol-1))
        else:
            colstr = mks(col)
            try:
                if self.case_sensitive:
                    mess = "column name '%s' not found (case sensitive)" % col
                    colnum = self._colnames.index(colstr)
                else:
                    mess \
                        = "column name '%s' not found (case insensitive)" % col
                    colnum = self._colnames_lower.index(colstr.lower())
            except ValueError: