matplotlib/matplotlib · error · TypeError

tz must be string or tzinfo subclass, not {tz!r}.

Error message

tz must be string or tzinfo subclass, not {tz!r}.

What it means

Error "tz must be string or tzinfo subclass, not {tz!r}." thrown in matplotlib/matplotlib.

Source

Thrown at lib/matplotlib/dates.py:224

def _get_tzinfo(tz=None):
    """
    Generate `~datetime.tzinfo` from a string or return `~datetime.tzinfo`.
    If None, retrieve the preferred timezone from the rcParams dictionary.
    """
    tz = mpl._val_or_rc(tz, 'timezone')
    if tz == 'UTC':
        return UTC
    if isinstance(tz, str):
        tzinfo = dateutil.tz.gettz(tz)
        if tzinfo is None:
            raise ValueError(f"{tz} is not a valid timezone as parsed by"
                             " dateutil.tz.gettz.")
        return tzinfo
    if isinstance(tz, datetime.tzinfo):
        return tz
    raise TypeError(f"tz must be string or tzinfo subclass, not {tz!r}.")


# Time-related constants.
EPOCH_OFFSET = float(datetime.datetime(1970, 1, 1).toordinal())
# EPOCH_OFFSET is not used by matplotlib
MICROSECONDLY = SECONDLY + 1
HOURS_PER_DAY = 24.
MIN_PER_HOUR = 60.
SEC_PER_MIN = 60.
MONTHS_PER_YEAR = 12.

DAYS_PER_WEEK = 7.
DAYS_PER_MONTH = 30.
DAYS_PER_YEAR = 365.0

MINUTES_PER_DAY = MIN_PER_HOUR * HOURS_PER_DAY

SEC_PER_HOUR = SEC_PER_MIN * MIN_PER_HOUR

View on GitHub (pinned to b379c1b69e)

When it happens

Trigger: Thrown at lib/matplotlib/dates.py:224 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/9aae22a28f4f3784. Report an issue: GitHub.