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timedelta-isoformat

The timedelta-isoformat library provides supplemental ISO 8601 duration support to the datetime.timedelta class.

The library is pure-Python, and does not depend upon regular expressions.

Functionality is provided in a subclass of datetime.timedelta that implements additional isoformat() and fromisoformat(duration_string) methods.

Usage

>>> from timedelta_isoformat import timedelta
>>> from datetime import datetime
>>>
>>> first = datetime(year=2022, month=10, day=2)
>>> second = datetime(year=2022, month=11, day=27, hour=14)
>>>
>>> td = timedelta(seconds=(second - first).total_seconds())
>>> td.isoformat()
'PT1358H'
>>>
>>> first + timedelta.fromisoformat('PT1358H')
datetime.datetime(2022, 11, 27, 14, 0)

Design decisions

A variety of ISO 8601 duration parsers exist across a range of programming languages, and many of them have made slightly different design decisions.

Some of the significant design decisions made within this library are:

  • Values in parsed duration strings must be zero-or-greater (PT1H is considered valid; P-2D is not)
  • Time deltas must be zero-or-greater to be formatted as ISO durations (timedelta(hours=-1, seconds=5200) can be formatted; timedelta(hours=-1, seconds=2400) cannot)
  • Empty time segments at the end of duration strings are allowed (P1DT is considered valid)
  • Measurement limits are checked within date/time segments (PT20:59:01 is within limits; PT20:60:01 is not)
  • Measurement values are parsed into floating-point values (at the time of writing, precise procedural algorithms to parse base-ten strings into integers for large inputs are not practical -- or not widely known)
  • When inputs are reliably known to be of correct type and format, assertions should be safe to remove (for example, by including the -O command-line flag when invoking the Python interpreter) to improve runtime performance