Daniel Lenski <dlen...@gmail.com> added the comment:
Like many others here, I've run into this issue because I'm trying to parse timestamps from JSON. (Specifically, I'm trying to parse timestamps from JSON serialization of Java POJOs and/or Kotlin data classes, as serialized by the Jackson serialization library for JVM languages, in conjunction with JavaTimeModule. https://fasterxml.github.io/jackson-modules-java8/javadoc/datetime/2.9/com/fasterxml/jackson/datatype/jsr310/JavaTimeModule.html) In order to "be lenient in what I accept" (adhering to the robustness principal), I need to add a special case for deserialization of strings ending with 'Z'. This gets pretty tricky and pretty subtle quickly. Here is my Python 3.7+ code path (the strptime-based code path for earlier versions is much, much uglier). from numbers import Number from datetime import datetime, timezone def number_or_iso8601_to_dt(ts, t=datetime): if isinstance(ts, Number): return datetime.utcfromtimestamp(ts).replace(tzinfo=timezone.utc) elif ts.endswith('Z'): # This is not strictly correct, since it would accept a string with # two timezone specifications (e.g. ending with +01:00Z) and # silently pass that erroneous representation: # # return datetime.fromisoformat(ts[:-1]).replace(tzinfo=timezone.utc) # # This version is better: d = datetime.fromisoformat(ts[:-1]) if d.tzinfo is not None: raise ValueError(f"time data '{ts}' contains multiple timezone suffixes") return d.replace(tzinfo=timezone.utc) else: return datetime.fromisoformat(ts) I don't really understand why .fromisoformat() must be *strictly* the inverse of .isoformat(). As @mehaase points out, the transformation isn't strictly reversible as is. There are other functions where the Python standard library has special-cased options for extremely common use cases. For example, `str.split(None)`, which is certainly not the inverse of the non-existent `None.join()`. This feels to me like a case where the standard library should simply just accept an extremely-common real-world variant in the interests of interoperability. I would also be in favor of @p-ganssle's proposal (3), wherein `datetime.isoformat` would also output the 'Z' suffix for the UTC timezone. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue35829> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
