idea: allow passing ISO string to all constructors

[ariebovenberg]

Something that has been bouncing around my mind: what if all constructors accepted an ISO string als an 'alternative' way of constructing an object?

So you could do:

PlainDateTime(2020, 3, 2, 8, 15)
# but also equivalently
PlainDateTime("2020-03-02 08:15")

pros:

• More readable than comma separated integers
• Great for specifying literals in tests (speaking from experience)
• Makes it possible to have a round-trippable repr() (see Allow recreating from repr #222)
• It's a somewhat popular pattern. Other libraries do it (Temporal, Arrow.get()), and Pydantic has proven the "constructor is parser" pattern is successful (aside from whether this is a good thing)
• It's faster—really. Python's object overhead is so large that it's actually faster in most cases to parse the values from one string object instead of handling individual integers.
• Instant now has a constructor, instead of awkwardly not
• shorter to type (no method name needed)

cons. There aren't many, but they're big ones:

• There are now two ways of parsing an ISO string. The constructor and parse_common_iso()
• It makes the constructor more complex from a typing perspective which may confuse users not used to seeing "overloads"
• "Parsing" and "constructing an object" are conceptually different. Combining the two could lead to muddied semantics.

[dycw]

This is extremely useful. In pandas, I find myself reaching for pd.Timestamp("...") a heck of a lot more than pd.Timestamp(2025, ...).