python/cpython · error · ValueError

second must be in 0..59, not {second}

Error message

second must be in 0..59, not {second}

What it means

Raised by _check_time_fields() when the second argument to time()/datetime() is not in 0..59. Notably, second=60 (a leap second) is invalid: CPython's datetime does not represent leap seconds, so UTC times like 23:59:60 must be handled before construction.

Source

Thrown at Lib/_pydatetime.py:591

        raise ValueError(f"year must be in {MINYEAR}..{MAXYEAR}, not {year}")
    if not 1 <= month <= 12:
        raise ValueError(f"month must be in 1..12, not {month}")
    dim = _days_in_month(year, month)
    if not 1 <= day <= dim:
        raise ValueError(f"day {day} must be in range 1..{dim} for month {month} in year {year}")
    return year, month, day

def _check_time_fields(hour, minute, second, microsecond, fold):
    hour = _index(hour)
    minute = _index(minute)
    second = _index(second)
    microsecond = _index(microsecond)
    if not 0 <= hour <= 23:
        raise ValueError(f"hour must be in 0..23, not {hour}")
    if not 0 <= minute <= 59:
        raise ValueError(f"minute must be in 0..59, not {minute}")
    if not 0 <= second <= 59:
        raise ValueError(f"second must be in 0..59, not {second}")
    if not 0 <= microsecond <= 999999:
        raise ValueError(f"microsecond must be in 0..999999, not {microsecond}")
    if fold not in (0, 1):
        raise ValueError(f"fold must be either 0 or 1, not {fold}")
    return hour, minute, second, microsecond, fold

def _check_tzinfo_arg(tz):
    if tz is not None and not isinstance(tz, tzinfo):
        raise TypeError(
            "tzinfo argument must be None or of a tzinfo subclass, "
            f"not {type(tz).__name__!r}"
        )

def _divide_and_round(a, b):
    """divide a by b and round result to the nearest integer

    When the ratio is exactly half-way between two integers,
    the even integer is returned.

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Convert leap seconds to second=59 with an extra-second flag, or smear, before constructing datetime
2. Use divmod carry: sec, rem = divmod(sec, 60) and add rem to minutes
3. Validate 0 <= second <= 59 in ingestion parsers

Example fix

// before
dt = datetime(2016, 12, 31, 23, 59, 60)  # leap second -> ValueError
// after
if sec == 60:
    dt = datetime(2016, 12, 31, 23, 59, 59)  # flag leap second separately
else:
    dt = datetime(2016, 12, 31, 23, 59, sec)

if not 0 <= second <= 59:
    raise ValueError('second must be 0..59 (leap seconds unsupported)')

def valid_second(s) -> bool:
    return 0 <= s <= 59

When it happens

Trigger: time(23, 59, 60); parsing GPS/NTP or UTC timestamps during an inserted leap second; carrying 60 from sub-second rounding logic.

Common situations: Ingesting UTC time series or satellite/GPS data that contains :60 seconds; smearing or rounding bugs that produce second=60; test fixtures copied from leap-second tables.

Related errors

• hour must be in 0..23, not {hour}
• minute must be in 0..59, not {minute}
• microsecond must be in 0..999999, not {microsecond}
• month must be in 1..12, not {month}
• day {day} must be in range 1..{dim} for month {month} in yea

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/b3b25da094af5419. Report an issue: GitHub.