ciso8601
Fast ISO8601 date time parser for Python written in C
Decision gist · record as of 2026-08-14
Yes, if you parse ISO 8601 or RFC 3339 strings in a performance-sensitive context and can tolerate the C extension dependency. The compiled wheels cover common platforms, and the library is actively maintained. However, if you're on Python 3.11+ and performance is not critical, the built-in datetime module may be sufficient and simpler. No known security vulnerabilities.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires a C compiler or pre-built wheel for your platform; some architectures may not have wheels available.
- Medium install friction due to compiled C extension requiring platform-specific wheels.
- Wheels are available for common platforms (macOS, Linux, Windows) across Python 3.10–3.12, but installation may require a C compiler on unsupported architectures.
License · maintenance · safety
MIT (permissive) — MIT license is permissive and places no restrictions on use, modification, or distribution in proprietary or open-source projects.
last release 2025-08-20 (359 days) · last repo commit 2026-06-11 · 576 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 11,792,032 downloads/mo, #1,362 on PyPI
Alternatives
Verify before relying
pip install ciso8601
import ciso8601
dt = ciso8601.parse_datetime('2014-12-05T12:30:45.123456-05:30')
print(dt) # datetime.datetime(2014, 12, 5, 12, 30, 45, 123456, tzinfo=...)- Whether backports.datetime_fromisoformat or the built-in datetime module in Python 3.11+ are sufficient for your use case instead.
- Exact performance gains in your specific workload; benchmarks show nanosecond-scale differences that may not matter outside tight loops.
What it is and what it does
ciso8601 is a C extension that converts ISO 8601 and RFC 3339 date-time strings into Python datetime objects. It is designed as a high-performance alternative to pure-Python parsers, with no runtime dependencies beyond Python itself. The library parses a subset of ISO 8601 that covers the most common use cases—basic and extended formats with optional time zone information—and returns either a timezone-aware or naive datetime depending on the input.
The package offers strict error handling: parse_datetime() either returns a valid datetime or raises ValueError with a description of why the string doesn't conform to the supported subset. It is tested across Python 2.7 and 3.4–3.14, though the C extension requires pre-built wheels or a compiler at install time. The documentation notes that since Python 3.11, the built-in datetime module has improved significantly, and ciso8601 may not be necessary for all use cases.
Use it for
- Parse timestamps in high-throughput APIs or data pipelines where nanosecond-scale performance gains matter.
- Deserialize ISO 8601 timestamps from JSON or other structured data formats in performance-critical applications.
- Handle RFC 3339 timestamps from web services or logs when speed is a requirement.
- Replace slower pure-Python date parsers in existing codebases without changing the calling interface.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes, if you parse ISO 8601 or RFC 3339 strings in a performance-sensitive context and can tolerate the C extension dependency.
The compiled wheels cover common platforms, and the library is actively maintained. However, if you're on Python 3.11+ and performance is not critical, the built-in datetime module may be sufficient and simpler. No known security vulnerabilities.
Install
ciso8601 on PyPI
Before you install
Medium install friction due to compiled C extension requiring platform-specific wheels. Wheels are available for common platforms (macOS, Linux, Windows) across Python 3.10–3.12, but installation may require a C compiler on unsupported architectures. Maintenance is active with recent releases.
Requires a C compiler or pre-built wheel for your platform; some architectures may not have wheels available.
License in practice
MIT license is permissive and places no restrictions on use, modification, or distribution in proprietary or open-source projects.
Quickstart
pip install ciso8601
import ciso8601
dt = ciso8601.parse_datetime('2014-12-05T12:30:45.123456-05:30')
print(dt) # datetime.datetime(2014, 12, 5, 12, 30, 45, 123456, tzinfo=...)Verify before relying
- Whether backports.datetime_fromisoformat or the built-in datetime module in Python 3.11+ are sufficient for your use case instead.
- Exact performance gains in your specific workload; benchmarks show nanosecond-scale differences that may not matter outside tight loops.
Package facts
| License | MIT permissive |
| Python support | Not specified |
| Install friction | Medium. Platform-specific wheel |
| Runtime dependencies | None |
| Maintenance | Actively maintained 359 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 11,792,032 / month, #1,362 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Intended Audience :: DevelopersLicense :: OSI Approved :: MIT LicenseOperating System :: OS IndependentProgramming Language :: PythonProgramming Language :: Python :: 2Programming Language :: Python :: 2.7Programming Language :: Python :: 3Programming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Programming Language :: Python :: 3.14Programming Language :: Python :: 3.4Programming Language :: Python :: 3.5Programming Language :: Python :: 3.6Programming Language :: Python :: 3.7Programming Language :: Python :: 3.8Programming Language :: Python :: 3.9Topic :: Software Development :: Libraries :: Python Modules |
Evidence: ciso8601-2.3.3-cp310-cp310-macosx_11_0_arm64.whl; ciso8601-2.3.3-cp310-cp310-macosx_11_0_universal2.whl; ciso8601-2.3.3-cp310-cp310-macosx_11_0_x86_64.whl; ciso8601-2.3.3-cp310-cp310-manylinux1_x86_64.manylinux_2_28_x86_64.manylinux_2_5_x86_64.whl; ciso8601-2.3.3-cp310-cp310-manylinux2014_aarch64.manylinux_2_17_aarch64.manylinux_2_28_aarch64.whl; ciso8601-2.3.3-cp310-cp310-musllinux_1_2_aarch64.whl; ciso8601-2.3.3-cp310-cp310-musllinux_1_2_x86_64.whl; ciso8601-2.3.3-cp310-cp310-win_amd64.whl; ciso8601-2.3.3-cp311-cp311-macosx_11_0_arm64.whl; ciso8601-2.3.3-cp311-cp311-macosx_11_0_universal2.whl; ciso8601-2.3.3-cp311-cp311-macosx_11_0_x86_64.whl; ciso8601-2.3.3-cp311-cp311-manylinux1_x86_64.manylinux_2_28_x86_64.manylinux_2_5_x86_64.whl; ciso8601-2.3.3-cp311-cp311-manylinux2014_aarch64.manylinux_2_17_aarch64.manylinux_2_28_aarch64.whl; ciso8601-2.3.3-cp311-cp311-musllinux_1_2_aarch64.whl; ciso8601-2.3.3-cp311-cp311-musllinux_1_2_x86_64.whl; ciso8601-2.3.3-cp311-cp311-win_amd64.whl; ciso8601-2.3.3-cp312-cp312-macosx_11_0_arm64.whl; ciso8601-2.3.3-cp312-cp312-macosx_11_0_universal2.whl; ciso8601-2.3.3-cp312-cp312-macosx_11_0_x86_64.whl; ciso8601-2.3.3-cp312-cp312-manylinux1_x86_64.manylinux_2_28_x86_64.manylinux_2_5_x86_64.whl
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See also iso8601 · isodate · aniso8601 · backports-datetime-fromisoformat · udatetime · pyRFC3339 · tonyg-rfc3339 · metomi-isodatetime · isoduration · rfc3339