From 39cdd6a6769fdc965aa8e7c5c8576e68c14f70b6 Mon Sep 17 00:00:00 2001
From: Alan <njshk@163.com>
Date: Thu, 1 Oct 2026 08:09:37 +0800
Subject: [PATCH] Reject ISO durations with missing components

---
 src/environs/fields.py |  4 ++--
 tests/test_environs.py | 17 +++++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/environs/fields.py b/src/environs/fields.py
index 3d36af6..bba9146 100644
--- a/src/environs/fields.py
+++ b/src/environs/fields.py
@@ -74,10 +74,10 @@ class TimeDelta(fields.TimeDelta):
     _ISO_8601_REGEX = re.compile(
         r"^(?:\s*)"  # optional leading whitespace
         r"(?P<sign>[+-]?)"  # optional sign
-        r"P"  # designator
+        r"P(?=\d|T\d)"  # designator followed by at least one component
         r"(?:(?P<weeks>\d+(?:\.\d+)?)W|"  # weeks variant
         r"(?:(?P<days>\d+(?:\.\d+)?)D)?"  # days
-        r"(?:T"  # time designator
+        r"(?:T(?=\d)"  # time designator must be followed by a component
         r"(?:(?P<hours>\d+(?:\.\d+)?)H)?"  # hours
         r"(?:(?P<minutes>\d+(?:\.\d+)?)M)?"  # minutes
         r"(?:(?P<seconds>\d+(?:\.\d+)?)S)?"  # seconds (can be fractional)
diff --git a/tests/test_environs.py b/tests/test_environs.py
index 7baf13c..7cfef05 100644
--- a/tests/test_environs.py
+++ b/tests/test_environs.py
@@ -355,6 +355,23 @@ def test_timedelta_cast(self, set_env, env: environs.Env):
         set_env({"TIMEDELTA": "PT0S"})
         assert env.timedelta("TIMEDELTA", format="iso8601") == dt.timedelta()
 
+    @pytest.mark.parametrize(
+        "value", ["P", "PT", "+P", "-PT", " P ", " PT ", "P1DT", "P0DT", "-P1DT"]
+    )
+    def test_timedelta_iso8601_requires_components(
+        self, value, set_env, env: environs.Env
+    ):
+        set_env({"TIMEDELTA": value})
+        with pytest.raises(
+            environs.EnvValidationError, match="Not a valid period of time"
+        ):
+            env.timedelta("TIMEDELTA", format="iso8601")
+
+    @pytest.mark.parametrize("value", ["P0W", "P0D", "PT0H", "PT0M", "PT0S", "P0DT0S"])
+    def test_timedelta_iso8601_zero_components(self, value, set_env, env: environs.Env):
+        set_env({"TIMEDELTA": value})
+        assert env.timedelta("TIMEDELTA", format="iso8601") == dt.timedelta()
+
     def test_time_cast(self, set_env, env: environs.Env):
         set_env({"TIME": "10:30"})
         assert env.time("TIME") == dt.time(hour=10, minute=30, second=0)