Force non-datetime columns to be read as such.
    Supports both string formatted and integer timestamp columns.

def _parse_date_columns(data_frame, parse_dates):
    """
    Force non-datetime columns to be read as such.
    Supports both string formatted and integer timestamp columns.
    """
    parse_dates = _process_parse_dates_argument(parse_dates)

    # we want to coerce datetime64_tz dtypes for now to UTC
    # we could in theory do a 'nice' conversion from a FixedOffset tz
    # GH11216
    for col_name, df_col in data_frame.iteritems():
        if is_datetime64tz_dtype(df_col) or col_name in parse_dates:
            try:
                fmt = parse_dates[col_name]
            except TypeError:
                fmt = None
            data_frame[col_name] = _handle_date_column(df_col, format=fmt)

    return data_frame