fix(#47): count step values from the field minimum

pycron/__init__.py

@@ -37,7 +37,9 @@ def _to_int(value: Any, allow_daynames: bool = False) -> int:
     raise ValueError("Failed to parse string to integer")
 
 
-def _parse_arg(value: str, target: int, allow_daynames: bool = False) -> bool:
+def _parse_arg(
+    value: str, target: int, allow_daynames: bool = False, min_value: int = 0
+) -> bool:
     """
     Parses a given value and checks if it matches the provided target.
     Allowing day names is optional, but can be useful for certain situations.
@@ -46,6 +48,8 @@ def _parse_arg(value: str, target: int, allow_daynames: bool = False) -> bool:
         value = value to parse and check
         target = target value to compare with
         allow_daynames = True, to allow values like Mon or Monday
+        min_value = smallest value the field accepts, used as the
+                    starting point for step values like */2
     @output: True if the value matches the target, False otherwise
     """
     # pylint: disable=too-many-branches
@@ -99,8 +103,10 @@ def _parse_arg(value: str, target: int, allow_daynames: bool = False) -> bool:
             # Not sure if applicable for every situation, but just to make sure...
             if v != "*":
                 continue
-            # If the remainder is zero, this matches
-            if target % _to_int(interval, allow_daynames=allow_daynames) == 0:
+            # Steps count from the start of the field, not from zero,
+            # so */2 on a 1-based field means 1, 3, 5... not 2, 4, 6...
+            interval_int = _to_int(interval, allow_daynames=allow_daynames)
+            if (target - min_value) % interval_int == 0:
                 return True
 
     return False
@@ -124,18 +130,18 @@ def is_now(s: str, dt: Optional[datetime] = None) -> bool:
     # Special case if both of the 'day' -fields are set -> allow either one to match
     # See: https://github.com/kipe/pycron/issues/29
     if "*" not in dom and "*" not in dow:
-        day_rule = _parse_arg(dom, dt.day) or _parse_arg(
+        day_rule = _parse_arg(dom, dt.day, min_value=1) or _parse_arg(
             dow, 0 if weekday == 7 else weekday, True
         )
     else:
-        day_rule = _parse_arg(dom, dt.day) and _parse_arg(
+        day_rule = _parse_arg(dom, dt.day, min_value=1) and _parse_arg(
             dow, 0 if weekday == 7 else weekday, True
         )
 
     return (
         _parse_arg(minute, dt.minute)
         and _parse_arg(hour, dt.hour)
-        and _parse_arg(month, dt.month)
+        and _parse_arg(month, dt.month, min_value=1)
         and day_rule
     )
 

tests/test_dom.py

@@ -13,7 +13,9 @@ def test_dom(self):
         def run(now):
             assert pycron.is_now("* * * * *", now)
             assert pycron.is_now("* * 18 * *", now)
-            assert pycron.is_now("* * */6 * *", now)
+            # Steps count from the 1st, so */6 is the 1st, 7th, 13th, 19th...
+            # and the 18th is not one of those.
+            assert pycron.is_now("* * */6 * *", now) is False
             assert pycron.is_now("* * 1,16,18 * *", now)
             assert pycron.is_now("* * 19 * *", now) is False
             assert pycron.is_now("* * */4 * *", now) is False
@@ -29,3 +31,11 @@ def run(now):
         run(arrow.get(now))
         run(udatetime.from_string(now.isoformat()))
         run(Delorean(datetime=now, timezone="UTC").datetime)
+
+    def test_dom_step(self):
+        # */6 is just a shorthand for 1-31/6, both start counting from the 1st.
+        assert pycron.is_now("* * */6 * *", datetime(2015, 6, 1, 16, 7))
+        assert pycron.is_now("* * */6 * *", datetime(2015, 6, 7, 16, 7))
+        assert pycron.is_now("* * */6 * *", datetime(2015, 6, 19, 16, 7))
+        assert pycron.is_now("* * */6 * *", datetime(2015, 6, 6, 16, 7)) is False
+        assert pycron.is_now("* * 1-31/6 * *", datetime(2015, 6, 7, 16, 7))

tests/test_month.py

@@ -13,10 +13,12 @@ def test_parser(self):
         def run(now):
             assert pycron.is_now("* * * * *", now)
             assert pycron.is_now("* * * 6 *", now)
-            assert pycron.is_now("* * * */2 *", now)
+            # Steps count from January, so */2 is Jan, Mar, May... and */5 is
+            # Jan, Jun, Nov. June matches the second one, not the first.
+            assert pycron.is_now("* * * */2 *", now) is False
             assert pycron.is_now("* * * 1,4,6,12 *", now)
             assert pycron.is_now("* * * 5 *", now) is False
-            assert pycron.is_now("* * * */5 *", now) is False
+            assert pycron.is_now("* * * */5 *", now)
             assert pycron.is_now("* * * 1,4,12 *", now) is False
             assert pycron.MONTH_CHOICES[now.month - 1][1] == "June"
             assert pycron.is_now("* * * 5-8 *", now)
@@ -29,3 +31,11 @@ def run(now):
         run(arrow.get(now))
         run(udatetime.from_string(now.isoformat()))
         run(Delorean(datetime=now, timezone="UTC").datetime)
+
+    def test_month_step(self):
+        # */3 is just a shorthand for 1-12/3, both start counting from January.
+        assert pycron.is_now("* * * */3 *", datetime(2015, 1, 18, 16, 7))
+        assert pycron.is_now("* * * */3 *", datetime(2015, 4, 18, 16, 7))
+        assert pycron.is_now("* * * */3 *", datetime(2015, 7, 18, 16, 7))
+        assert pycron.is_now("* * * */3 *", datetime(2015, 6, 18, 16, 7)) is False
+        assert pycron.is_now("* * * 1-12/3 *", datetime(2015, 4, 18, 16, 7))