ENH: Multiple values to at/on in cond API

docs/code/conds/api/periodical_restricted.py

@@ -16,10 +16,18 @@ def do_between():
 def do_at():
     ...
 
+@app.task(daily.at("08:00", "12:00", "18:00"))
+def do_at_multiple():
+    ...
+
 @app.task(weekly.on("Monday"))
 def do_on():
     ...
 
+@app.task(weekly.on("Monday", "Friday", "Sunday"))
+def do_on_multiple():
+    ...
+
 @app.task(monthly.starting("3rd"))
 def do_starting():
     ...

docs/handbooks/conditions/api/periodical.rst

@@ -88,6 +88,13 @@ and *starting Friday* means the week is set to start on Friday.
     ``between Monday and Friday`` means Monday at 00:00
     (0 am) to Friday 24:00 (12 pm).
 
+.. note::
+
+    Passing multiple values to *at/on* is a convenient way to schedule
+    a task to run at multiple times. For example, ``weekly.on("Mon", "Fri")`` 
+    is the same as ``weekly.on("Mon") | weekly.on("Fri")`` and it can be used
+    to run a task on Mondays and Fridays.
+
 There are also **time of ...** conditions check if the current time
 is within the given period.
 

rocketry/conditions/api.py

@@ -1,3 +1,4 @@
+from functools import reduce
 from typing import Callable, Union
 from rocketry.conditions import (
     DependFailure, DependFinish, DependSuccess, TaskFailed, 
@@ -45,14 +46,24 @@ def after(self, start):
         period = self._cls_period(start, None)
         return self._get_cond(period)
 
-    def on(self, span):
+    def on(self, *spans):
         # Alias for "at"
-        return self.at(span)
+        return self.at(*spans)
 
-    def at(self, span):
+    def at(self, span, *spans):
         # Alias for "on"
-        period = self._cls_period(span, time_point=True)
-        return self._get_cond(period)
+        n_spans = len(spans)
+        if n_spans == 0:
+            # Called like: daily.at("10:00")
+            period = self._cls_period(span, time_point=True)
+            return self._get_cond(period)
+        else:
+            # Called like: daily.at("10:00", "12:00")
+            conds = []
+            for span in (span, *spans):
+                cond = self.at(span)
+                conds.append(cond)
+            return reduce(lambda a, b: a | b, conds)
 
     def starting(self, start):
         period = self._cls_period.starting(start)

rocketry/test/condition/test_api.py

@@ -82,6 +82,8 @@
 
     pytest.param(daily.at("23:00:00"), TaskExecutable(period=TimeOfDay("23:00:00", "00:00:00")), id="daily at end"),
     pytest.param(daily.at("23:00:01"), TaskExecutable(period=TimeOfDay("23:00:01", "00:00:01")), id="daily at specific"),
+
+    pytest.param(weekly.at("Mon", "Wed", "Fri"), TaskExecutable(period=TimeOfWeek("Monday", time_point=True)) | TaskExecutable(period=TimeOfWeek("Wednesday", time_point=True)) | TaskExecutable(period=TimeOfWeek("Friday", time_point=True)), id="weekly at (multiple)"),
 ]
 
 params_pipeline = [
@@ -165,3 +167,5 @@ def test_observe(cond, session):
 def test_fail():
     with pytest.raises(ValueError):
         every("5 seconds", based="oops")
+    with pytest.raises(TypeError):
+        daily.at()