feat: add validator argument

envier/env.py

@@ -48,6 +48,7 @@ def __init__(
         type,  # type: Union[object, Type[T]]
         name,  # type: str
         parser=None,  # type: Optional[Callable[[str], T]]
+        validator=None,  # type: Optional[Callable[[T], None]]
         map=None,  # type: Optional[MapType]
         default=NoDefault,  # type: Union[T, NoDefaultType]
         deprecations=None,  # type: Optional[List[DeprecationInfo]]
@@ -63,11 +64,12 @@ def __init__(
         self.type = type
         self.name = name
         self.parser = parser
+        self.validator = validator
         self.map = map
         self.default = default
         self.deprecations = deprecations
 
-    def __call__(self, env, prefix):
+    def _retrieve(self, env, prefix):
         # type: (Env, str) -> T
         source = env.source
 
@@ -142,6 +144,15 @@ def __call__(self, env, prefix):
 
         return self.type(raw)  # type: ignore[call-arg,operator]
 
+    def __call__(self, env, prefix):
+        # type: (Env, str) -> T
+        value = self._retrieve(env, prefix)
+
+        if self.validator is not None:
+            self.validator(value)
+
+        return value
+
 
 class DerivedVariable(Generic[T]):
     def __init__(self, type, derivation):
@@ -234,25 +245,27 @@ def var(
         type,  # type: Type[T]
         name,  # type: str
         parser=None,  # type: Optional[Callable[[str], T]]
+        validator=None,  # type: Optional[Callable[[T], None]]
         map=None,  # type: Optional[MapType]
         default=NoDefault,  # type: Union[T, NoDefaultType]
         deprecations=None,  # type: Optional[List[DeprecationInfo]]
     ):
         # type: (...) -> EnvVariable[T]
-        return EnvVariable(type, name, parser, map, default, deprecations)
+        return EnvVariable(type, name, parser, validator, map, default, deprecations)
 
     @classmethod
     def v(
         cls,
         type,  # type: Union[object, Type[T]]
         name,  # type: str
         parser=None,  # type: Optional[Callable[[str], T]]
+        validator=None,  # type: Optional[Callable[[T], None]]
         map=None,  # type: Optional[MapType]
         default=NoDefault,  # type: Union[T, NoDefaultType]
         deprecations=None,  # type: Optional[List[DeprecationInfo]]
     ):
         # type: (...) -> EnvVariable[T]
-        return EnvVariable(type, name, parser, map, default, deprecations)
+        return EnvVariable(type, name, parser, validator, map, default, deprecations)
 
     @classmethod
     def der(cls, type, derivation):

tests/test_env.py

@@ -311,3 +311,29 @@ class DictConfig(Env):
         foo = Env.der(Optional[int], lambda _: value)
 
     assert DictConfig().foo is value
+
+
+@pytest.mark.parametrize(
+    "value,exc",
+    [
+        (0, None),
+        (512, None),
+        (-1, ValueError),
+        (513, ValueError),
+    ],
+)
+def test_env_validator(monkeypatch, value, exc):
+    monkeypatch.setenv("FOO", str(value))
+
+    class Config(Env):
+        def validate(value):
+            if not (0 <= value <= 512):
+                raise ValueError("Value must be between 0 and 512")
+
+        foo = Env.var(int, "FOO", validator=validate)
+
+    if exc is not None:
+        with pytest.raises(exc):
+            Config()
+    else:
+        assert Config().foo == value