Allow '0s', disallow '', allow negative integers

src/environs/__init__.py

@@ -32,15 +32,23 @@
 
 
 _EXPANDED_VAR_PATTERN = re.compile(r"(?<!\\)\$\{([A-Za-z0-9_]+)(:-[^\}:]*)?\}")
+# Ordered case-insensitive duration strings, loosely based on the [GEP-2257](https://gateway-api.sigs.k8s.io/geps/gep-2257/) spec
+# Discrepancies between this pattern and GEP-2257 duration strings:
+# - this pattern accepts units `w|d|h|m|s|ms|[uµ]s` (all units supported by the datetime.timedelta constructor), GEP-2257 accepts only `h|m|s|ms`
+# - this pattern allows for optional whitespace around the units, GEP-2257 does not
+# - this pattern is compiled to be case-insensitive, GEP-2257 expects lowercase units
+# - this pattern expects ordered (descending) units, GEP-2257 allows arbitrary order
+# - this pattern does not allow duplicate unit occurrences, GEP-2257 does
+# - this pattern allows for negative integers, GEP-2257 does not
 _TIMEDELTA_PATTERN = re.compile(
     r"^(?:\s*)"  # optional whitespace at the beginning of the string
-    r"(?:(\d+)\s*w\s*)?"  # weeks with optional whitespace around unit
-    r"(?:(\d+)\s*d\s*)?"  # days with optional whitespace around unit
-    r"(?:(\d+)\s*h\s*)?"  # hours with optional whitespace around unit
-    r"(?:(\d+)\s*m\s*)?"  # minutes with optional whitespace around unit
-    r"(?:(\d+)\s*s\s*)?"  # seconds with optional whitespace around unit
-    r"(?:(\d+)\s*ms\s*)?"  # milliseconds with optional whitespace around unit
-    r"(?:(\d+)\s*[µu]s\s*)?$",  # microseconds with optional whitespace around unit
+    r"(?:(-?\d+)\s*w\s*)?"  # weeks with optional whitespace around unit
+    r"(?:(-?\d+)\s*d\s*)?"  # days with optional whitespace around unit
+    r"(?:(-?\d+)\s*h\s*)?"  # hours with optional whitespace around unit
+    r"(?:(-?\d+)\s*m\s*)?"  # minutes with optional whitespace around unit
+    r"(?:(-?\d+)\s*s\s*)?"  # seconds with optional whitespace around unit
+    r"(?:(-?\d+)\s*ms\s*)?"  # milliseconds with optional whitespace around unit
+    r"(?:(-?\d+)\s*[µu]s\s*)?$",  # microseconds with optional whitespace around unit
     flags=re.IGNORECASE,
 )
 
@@ -373,15 +381,15 @@ def _deserialize(self, value, *args, **kwargs) -> timedelta:
         if isinstance(value, timedelta):
             return value
         match = _TIMEDELTA_PATTERN.match(value)
-        if match is not None and any(groups := match.groups(default=0)):
+        if match is not None and match.group(0):  # disallow "", allow "0s"
             return timedelta(
-                weeks=int(groups[0]),
-                days=int(groups[1]),
-                hours=int(groups[2]),
-                minutes=int(groups[3]),
-                seconds=int(groups[4]),
-                milliseconds=int(groups[5]),
-                microseconds=int(groups[6]),
+                weeks=int(match.group(1) or 0),
+                days=int(match.group(2) or 0),
+                hours=int(match.group(3) or 0),
+                minutes=int(match.group(4) or 0),
+                seconds=int(match.group(5) or 0),
+                milliseconds=int(match.group(6) or 0),
+                microseconds=int(match.group(7) or 0),
             )
         return super()._deserialize(value, *args, **kwargs)
 

tests/test_environs.py

@@ -229,13 +229,23 @@ def test_date_cast(self, set_env, env):
         assert env.date("DATE") == date
 
     def test_timedelta_cast(self, set_env, env):
+        # seconds as integer
+        set_env({"TIMEDELTA": "0"})
+        assert env.timedelta("TIMEDELTA") == dt.timedelta()
         set_env({"TIMEDELTA": "42"})
         assert env.timedelta("TIMEDELTA") == dt.timedelta(seconds=42)
+        set_env({"TIMEDELTA": "-42"})
+        assert env.timedelta("TIMEDELTA") == dt.timedelta(seconds=-42)
+        # seconds as duration string
+        set_env({"TIMEDELTA": "0s"})
+        assert env.timedelta("TIMEDELTA") == dt.timedelta()
         set_env({"TIMEDELTA": "42s"})
         assert env.timedelta("TIMEDELTA") == dt.timedelta(seconds=42)
+        set_env({"TIMEDELTA": "-42s"})
+        assert env.timedelta("TIMEDELTA") == dt.timedelta(seconds=-42)
         # whitespaces, case-insensitive, units subselection
-        set_env({"TIMEDELTA": " 42 D  42s "})
-        assert env.timedelta("TIMEDELTA") == dt.timedelta(days=42, seconds=42)
+        set_env({"TIMEDELTA": " 42 D  -42s "})
+        assert env.timedelta("TIMEDELTA") == dt.timedelta(days=42, seconds=-42)
         # unicode µs (in addition to us below)
         set_env({"TIMEDELTA": "42µs"})
         assert env.timedelta("TIMEDELTA") == dt.timedelta(microseconds=42)
@@ -250,6 +260,17 @@ def test_timedelta_cast(self, set_env, env):
             milliseconds=42,
             microseconds=42,
         )
+        # empty string not allowed
+        set_env({"TIMEDELTA": ""})
+        with pytest.raises(environs.EnvError):
+            env.timedelta("TIMEDELTA")
+        # float not allowed
+        set_env({"TIMEDELTA": "4.2"})
+        with pytest.raises(environs.EnvError):
+            env.timedelta("TIMEDELTA")
+        set_env({"TIMEDELTA": "4.2d"})
+        with pytest.raises(environs.EnvError):
+            env.timedelta("TIMEDELTA")
 
     def test_time_cast(self, set_env, env):
         set_env({"TIME": "10:30"})