matplotlib/matplotlib · error · TypeError

Unexpected type passed to {self!r}.

Error message

Unexpected type passed to {self!r}.

What it means

Error "Unexpected type passed to {self!r}." thrown in matplotlib/matplotlib.

Source

Thrown at lib/matplotlib/dates.py:938

        self._locator = locator

    def __call__(self, x, pos=None):
        try:
            locator_unit_scale = float(self._locator._get_unit())
        except AttributeError:
            locator_unit_scale = 1
        # Pick the first scale which is greater than the locator unit.
        fmt = next((fmt for scale, fmt in sorted(self.scaled.items())
                    if scale >= locator_unit_scale),
                   self.defaultfmt)

        if isinstance(fmt, str):
            self._formatter = DateFormatter(fmt, self._tz, usetex=self._usetex)
            result = self._formatter(x, pos)
        elif callable(fmt):
            result = fmt(x, pos)
        else:
            raise TypeError(f'Unexpected type passed to {self!r}.')

        return result


class rrulewrapper:
    """
    A simple wrapper around a `dateutil.rrule` allowing flexible
    date tick specifications.
    """
    def __init__(self, freq, tzinfo=None, **kwargs):
        """
        Parameters
        ----------
        freq : {YEARLY, MONTHLY, WEEKLY, DAILY, HOURLY, MINUTELY, SECONDLY}
            Tick frequency. These constants are defined in `dateutil.rrule`,
            but they are accessible from `matplotlib.dates` as well.
        tzinfo : `datetime.tzinfo`, optional
            Time zone information. The default is None.

View on GitHub (pinned to b379c1b69e)

When it happens

Trigger: Thrown at lib/matplotlib/dates.py:938 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of matplotlib/matplotlib@b379c1b69e (2026-08-21). Data as JSON: /api/errors/4537e6be14bdb829. Report an issue: GitHub.