python/cpython · error · ValueError

Inconsistent use of : in {found_dict[group_key]}

Error message

Inconsistent use of : in {found_dict[group_key]}

What it means

While post-processing a matched %z/%:z offset, _strptime normalizes colons out of the string; if the offset has a colon after the hours (z[3] == ':') it removes it, and then if seconds are present and the character at position 5 is not another ':', the format mixes colon and non-colon separators, raising this f-string ValueError showing the original matched group.

Source

Thrown at Lib/_strptime.py:704

                # U starts week on Sunday.
                week_of_year_start = 6
            else:
                # W starts week on Monday.
                week_of_year_start = 0
        elif group_key == 'V':
            iso_week = int(found_dict['V'])
        elif group_key in ('z', 'colon_z'):
            z = found_dict[group_key]
            if z:
                if z == 'Z':
                    gmtoff = 0
                else:
                    if z[3] == ':':
                        z = z[:3] + z[4:]
                        if len(z) > 5:
                            if z[5] != ':':
                                msg = f"Inconsistent use of : in {found_dict[group_key]}"
                                raise ValueError(msg)
                            z = z[:5] + z[6:]
                    hours = int(z[1:3])
                    minutes = int(z[3:5])
                    seconds = int(z[5:7] or 0)
                    gmtoff = (hours * 60 * 60) + (minutes * 60) + seconds
                    gmtoff_remainder = z[8:]
                    # Pad to always return microseconds.
                    gmtoff_remainder_padding = "0" * (6 - len(gmtoff_remainder))
                    gmtoff_fraction = int(gmtoff_remainder + gmtoff_remainder_padding)
                    if z.startswith("-"):
                        gmtoff = -gmtoff
                        gmtoff_fraction = -gmtoff_fraction
        elif group_key == 'Z':
            # Since -1 is default value only need to worry about setting tz if
            # it can be something other than -1.
            found_zone = found_dict['Z'].lower()
            for value, tz_values in enumerate(locale_time.timezone):
                if found_zone in tz_values:

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Normalize the offset string to either fully colon-separated '+HH:MM:SS' or fully compact '+HHMMSS' before parsing
2. Validate/repair offsets with a regex such as re.sub(r'(?<=\d{2}):(?=\d{2}(?!:))', '', s) to strip colons uniformly

Example fix

# before
>>> datetime.strptime('+05:0030', '%z')
ValueError: Inconsistent use of : in +05:0030

# after
>>> datetime.strptime('+050030', '%z')
datetime.datetime(2025, 8, 14, 0, 0, 30, tzinfo=datetime.timezone(datetime.timedelta(hours=5, seconds=30)))

import re

def normalize_offset(s: str) -> str:
    # make offset uniformly compact: +HH:MM:SS -> +HHMMSS
    return re.sub(r'(?<=[+-]\d{2}):(?=\d{2}(?!:))', '', s)

try:
    dt = datetime.strptime(s, '%z')
except ValueError as e:
    if 'Inconsistent use of :' in str(e):
        dt = datetime.strptime(normalize_offset(s), '%z')
    else:
        raise

When it happens

Trigger: An offset like '+05:0030' (colon between hours and minutes but not before seconds) parsed with %z/%:z — hours and minutes colon-separated while seconds are concatenated without one.

Common situations: Hand-built or corrupted timezone strings; concatenating offset parts with inconsistent separators; data from sources that emit '+HH:MMSS' malformed offsets.

Related errors

• Missing colon in %:z before '{rest}', got '{data_string}'
• timezone changed during initialization
• time data %r does not match format %r
• unconverted data remains: %s
• tzinfo subclass must override utcoffset()

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/da912549363debc1. Report an issue: GitHub.