Set the columns that should not undergo dtype conversions.

        Currently, any column that is involved with date parsing will not
        undergo such conversions.

def _set_noconvert_columns(self):
        """
        Set the columns that should not undergo dtype conversions.

        Currently, any column that is involved with date parsing will not
        undergo such conversions.
        """
        names = self.orig_names
        if self.usecols_dtype == 'integer':
            # A set of integers will be converted to a list in
            # the correct order every single time.
            usecols = list(self.usecols)
            usecols.sort()
        elif (callable(self.usecols) or
                self.usecols_dtype not in ('empty', None)):
            # The names attribute should have the correct columns
            # in the proper order for indexing with parse_dates.
            usecols = self.names[:]
        else:
            # Usecols is empty.
            usecols = None

        def _set(x):
            if usecols is not None and is_integer(x):
                x = usecols[x]

            if not is_integer(x):
                x = names.index(x)

            self._reader.set_noconvert(x)

        if isinstance(self.parse_dates, list):
            for val in self.parse_dates:
                if isinstance(val, list):
                    for k in val:
                        _set(k)
                else:
                    _set(val)

        elif isinstance(self.parse_dates, dict):
            for val in self.parse_dates.values():
                if isinstance(val, list):
                    for k in val:
                        _set(k)
                else:
                    _set(val)

        elif self.parse_dates:
            if isinstance(self.index_col, list):
                for k in self.index_col:
                    _set(k)
            elif self.index_col is not None:
                _set(self.index_col)