def _replace_nan ( a , val ) : mask = isnull ( a ) return where_method ( val , mask , a ) , mask
replace nan with none python
replace nan in a by val and returns the replaced array and the nan position
def _replace_nan(a, val):
    """
    replace nan in a by val, and returns the replaced array and the nan
    position
    """
    mask = isnull(a)
    return where_method(val, mask, a), mask