def _get_na_values(col, na_values, na_fvalues, keep_default_na):
if isinstance(na_values, dict):<EOL><INDENT>if col in na_values:<EOL><INDENT>return na_values[col], na_fvalues[col]<EOL><DEDENT>else:<EOL><INDENT>if keep_default_na:<EOL><INDENT>return _NA_VALUES, set()<EOL><DEDENT>return set(), set()<EOL><DEDENT><DEDENT>else:<EOL><INDENT>return na_values, na_fvalues<EOL><DEDENT>
Get the NaN values for a given column.

Parameters
----------
col : str
    The name of the column.
na_values : array-like, dict
    The object listing the NaN values as strings.
na_fvalues : array-like, dict
    The object listing the NaN values as floats.
keep_default_na : bool
    If `na_values` is a dict, and the column is not mapped in the
    dictionary, whether to return the default NaN values or the empty set.

Returns
-------
nan_tuple : A length-two tuple composed of

    1) na_values : the string NaN values for that column.
    2) na_fvalues : the float NaN values for that column.