Timedelta cannot be used in match statements

[user529481]

Bug report

Bug description:

Timedelta cannot be evaluated in match statements, see example below

from datetime import timedelta

td = timedelta(hours=1)

print(td == timedelta(hours=1)) # evaluates to True

match td:
    case timedelta(days=1):
        print('day')
    case timedelta(hours=1):
        print('hour')
    case _:
        print('unhandled') # prints `unhandled`

CPython versions tested on:

3.11

Operating systems tested on:

macOS

[terryjreedy]

Please add the traceback or if none, explain 'cannot be used'. What happens that you say this?

[ronaldoussoren]

The arguments in a match pattern are compared to attributes of the object, that is:

match td:
    case timedelta(hours=1):
         print("hour")

is more or less equivalent to:

if isinstance(td, timedelta) and hasattr(td, "hours") and td.hours == 1:
    print("hour")

Timedelta instances do not have a "hours" attributes. Changing this would be a backward incompatibility break, especially for the attributes days and seconds (timedelta(weeks=4).days == 28).

[zuo]

Perhaps adding milliseconds, minutes, hours, weeks as properties calculated on demand would "fix" the current (correct, yet unintuitive in this context) behavior – something along the lines:

    @property
    def milliseconds(self):
        return self.microseconds // 1000

    @property
    def minutes(self):
        return self.seconds // 60

    @property
    def hours(self):
        return self.seconds // 3600

    @property
    def weeks(self):
        return self.microseconds // 7

On the other hand, it could cause more confusion than benefit, considering that none of the current properties (days, seconds, microseconds) include the value of any other. (In general case, td.seconds != td.total_seconds())

And, obviously, it'd be a feature/enhancement, not a bugfix.

[zuo]

However, what can be done for sure, is an addition to the timedelta documentation – something like:

.. note::

   When referring to :meth:`~datetime.timedelta` instance attributes in keyword:`match`statements, as in ``case timedelta(seconds=42)``, you can use the actual attribute names only: :attr:`~datetime.timedelta.days`, :attr:`~datetime.timedelta.seconds` and :attr:`~datetime.timedelta.microseconds`.

[StanFromIreland]

There were similar discussions, #108631 and the idea did not receive much support.

Implementing is quite simple however, but then we are inconsistent, why should timedelta work but not date?

Subject: [PATCH] Make timedelta work with match
---
Index: Lib/_pydatetime.py
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/Lib/_pydatetime.py b/Lib/_pydatetime.py
--- a/Lib/_pydatetime.py	(revision 36ef3bfe39d767e283b55fe86f34e7671b7f5d1c)
+++ b/Lib/_pydatetime.py	(date 1741814383270)
@@ -645,6 +645,7 @@
     # was "Because I felt like it."
 
     __slots__ = '_days', '_seconds', '_microseconds', '_hashcode'
+    __match_args__ = ('weeks', 'days', 'hours', 'minutes', 'seconds', 'microseconds', 'milliseconds',)
 
     def __new__(cls, days=0, seconds=0, microseconds=0,
                 milliseconds=0, minutes=0, hours=0, weeks=0):
@@ -806,6 +807,26 @@
         """microseconds"""
         return self._microseconds
 
+    @property
+    def weeks(self):
+        """weeks"""
+        return self._days // 7
+
+    @property
+    def hours(self):
+        """hours"""
+        return self._seconds // 3600
+
+    @property
+    def minutes(self):
+        """minutes"""
+        return (self._seconds % 3600) // 60
+
+    @property
+    def milliseconds(self):
+        """milliseconds"""
+        return self._microseconds // 1000
+
     def __add__(self, other):
         if isinstance(other, timedelta):
             # for CPython compatibility, we cannot use

[StanFromIreland]

@pganssle What do you think? I doubt this will ever be implemented, like for the other ABCs.