---
id: metomi-isodatetime
version: "1!3.1.0"
license: LGPLv3
license_treatment: copyleft
maintenance: active
---

# metomi-isodatetime — Python ISO 8601 date time parser and data model/manipulation utilities

License: copyleft · Maintenance: active · Downloads: 78.6K/mo

## What it is and what it does

metomi-isodatetime is a full-specification ISO 8601 (2004) parser and data model library for Python. It provides parsers for dates, times, durations, and recurrence patterns, plus utilities to dump and format them. The package is designed to work similarly to Python's built-in datetime module but with complete ISO 8601 support, including extended year formats, week-based dates, ordinal dates, decimal fractions, and timezone offsets.

The library has no runtime dependencies and supports Python 3.7 through 3.11. It exposes both a Python API for programmatic use and a command-line interface for quick parsing and manipulation tasks. It is actively maintained, with recent commits and a stable production classification.

Use it for:

- Parse ISO 8601 date-time strings from APIs, logs, or data files into Python objects for manipulation.
- Calculate time intervals and apply durations to dates using ISO 8601 duration syntax (e.g., P1Y, PT3H).
- Generate recurring date sequences from ISO 8601 recurrence patterns (e.g., R/1999/P1Y).
- Format date-time objects back to ISO 8601 strings or custom formats using strftime-style templates.
- Work with extended year ranges (before year 0 or after year 9999) using expanded year syntax.

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

Parses and manipulates ISO 8601 date-time strings according to the 2004 specification, providing a Python API similar to the standard datetime module for working with dates, times, durations, and recurrences.

Yes. This package is worth installing if you need to parse or work with ISO 8601 date-time strings in a standards-compliant way. It has zero runtime dependencies, is actively maintained, supports current Python versions, and carries no known security vulnerabilities. The LGPLv3 license is permissive for most use cases. Install it if your application receives or generates ISO 8601 formatted dates.

## Install

pip install metomi-isodatetime
uv add metomi-isodatetime
poetry add metomi-isodatetime

## Installing metomi-isodatetime

Before you install: Installs cleanly with no runtime dependencies. Actively maintained with recent commits and stable production status across Python 3.7–3.11.

License in practice: Licensed under LGPLv3 (copyleft). You may use and modify the package freely, but any derivative work must also be distributed under LGPLv3 or a compatible license.

Quickstart:

pip install metomi-isodatetime

import metomi.isodatetime.parsers as parse
import metomi.isodatetime.dumpers as dump

date_time = parse.TimePointParser().parse('2000-01-01T00:00Z')
print(date_time.month_of_year)  # 1

duration = parse.DurationParser().parse('P1YT3H')
print(date_time + duration)  # <metomi.isodatetime.data.TimePoint: 2001-01-01T03:00:00Z>

## Package facts

- License: LGPLv3 (copyleft)
- Python support: supports_current
- Install friction: low
- Maintenance: active
- Downloads: 78.6K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

ISO 8601 date parser, datetime ISO format, parse ISO date time, ISO duration parser, date time recurrence, iso8601 python library, RFC date parsing, date-time-parsing, iso-8601, standards-compliant

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