Add config.from_env(as_=...) (#541)

* Add implementation and typing stub

* Add unit tests

* Update demo example

* Add typing tests

* Update changelog

* Update docs

* Add tests for an empty environment variable

* Improve wording in di_in_python.rst

* Update wording in changelog and docs

* Update doc blocks

README.rst

@@ -90,7 +90,7 @@ Key features of the ``Dependency Injector``:
        api_client = providers.Singleton(
            ApiClient,
            api_key=config.api_key,
-           timeout=config.timeout.as_int(),
+           timeout=config.timeout,
        )
 
        service = providers.Factory(
@@ -106,8 +106,8 @@ Key features of the ``Dependency Injector``:
 
    if __name__ == "__main__":
        container = Container()
-       container.config.api_key.from_env("API_KEY")
+       container.config.api_key.from_env("API_KEY", required=True)
-       container.config.timeout.from_env("TIMEOUT")
+       container.config.timeout.from_env("TIMEOUT", as_=int, default=5)
        container.wire(modules=[__name__])
 
        main()  # <-- dependency is injected automatically

docs/index.rst

@@ -96,7 +96,7 @@ Key features of the ``Dependency Injector``:
        api_client = providers.Singleton(
            ApiClient,
            api_key=config.api_key,
-           timeout=config.timeout.as_int(),
+           timeout=config.timeout,
        )
 
        service = providers.Factory(
@@ -112,8 +112,8 @@ Key features of the ``Dependency Injector``:
 
    if __name__ == "__main__":
        container = Container()
-       container.config.api_key.from_env("API_KEY")
+       container.config.api_key.from_env("API_KEY", required=True)
-       container.config.timeout.from_env("TIMEOUT")
+       container.config.timeout.from_env("TIMEOUT", as_=int, default=5)
        container.wire(modules=[__name__])
 
        main()  # <-- dependency is injected automatically

docs/introduction/di_in_python.rst

@@ -150,7 +150,7 @@ What does the Dependency Injector do?
 -------------------------------------
 
 With the dependency injection pattern objects loose the responsibility of assembling
-the dependencies. The ``Dependency Injector`` absorbs that responsibilities.
+the dependencies. The ``Dependency Injector`` absorbs that responsibility.
 
 ``Dependency Injector`` helps to assemble and inject the dependencies.
 
@@ -172,7 +172,7 @@ the dependency.
        api_client = providers.Singleton(
            ApiClient,
            api_key=config.api_key,
-           timeout=config.timeout.as_int(),
+           timeout=config.timeout,
        )
 
        service = providers.Factory(
@@ -188,8 +188,8 @@ the dependency.
 
    if __name__ == "__main__":
        container = Container()
-       container.config.api_key.from_env("API_KEY")
+       container.config.api_key.from_env("API_KEY", required=True)
-       container.config.timeout.from_env("TIMEOUT")
+       container.config.timeout.from_env("TIMEOUT", as_=int, default=5)
        container.wire(modules=[__name__])
 
        main()  # <-- dependency is injected automatically

docs/main/changelog.rst

@@ -9,6 +9,8 @@ follows `Semantic versioning`_
 
 Development version
 -------------------
+- Add argument ``as_`` to the ``config.from_env()`` method for the explicit type casting
+  of an environment variable value, e.g.: ``config.timeout.from_env("TIMEOUT", as_=int)``.
 - Add ``.providers`` attribute to the ``FactoryAggregate`` provider. It is an alias for
   ``FactoryAggregate.factories`` attribute.
 - Add ``.set_providers()`` method to the ``FactoryAggregate`` provider. It is an alias for

docs/providers/configuration.rst

@@ -205,6 +205,24 @@ Loading from an environment variable
    :lines: 3-
    :emphasize-lines: 18-20
 
+You can use ``as_`` argument for the type casting of an environment variable value:
+
+.. code-block:: python
+   :emphasize-lines: 2,6,10
+
+   # API_KEY=secret
+   container.config.api_key.from_env("API_KEY", as_=str, required=True)
+   assert container.config.api_key() == "secret"
+
+   # SAMPLING_RATIO=0.5
+   container.config.sampling.from_env("SAMPLING_RATIO", as_=float, required=True)
+   assert container.config.sampling() == 0.5
+
+   # TIMEOUT undefined, default is used
+   container.config.timeout.from_env("TIMEOUT", as_=int, default=5)
+   assert container.config.timeout() == 5
+
+
 Loading a value
 ---------------
 

examples/demo/with_di.py

@@ -13,7 +13,7 @@ class Container(containers.DeclarativeContainer):
     api_client = providers.Singleton(
         ApiClient,
         api_key=config.api_key,
-        timeout=config.timeout.as_int(),
+        timeout=config.timeout,
     )
 
     service = providers.Factory(
@@ -29,8 +29,8 @@ def main(service: Service = Provide[Container.service]):
 
 if __name__ == "__main__":
     container = Container()
-    container.config.api_key.from_env("API_KEY")
+    container.config.api_key.from_env("API_KEY", required=True)
-    container.config.timeout.from_env("TIMEOUT")
+    container.config.timeout.from_env("TIMEOUT", as_=int, default=5)
     container.wire(modules=[__name__])
 
     main()  # <-- dependency is injected automatically

src/dependency_injector/providers.pyi

@@ -205,7 +205,7 @@ class ConfigurationOption(Provider[Any]):
     def from_yaml(self, filepath: Union[Path, str], required: bool = False, loader: Optional[Any] = None, envs_required: bool = False) -> None: ...
     def from_pydantic(self, settings: PydanticSettings, required: bool = False, **kwargs: Any) -> None: ...
     def from_dict(self, options: _Dict[str, Any], required: bool = False) -> None: ...
-    def from_env(self, name: str, default: Optional[Any] = None, required: bool = False) -> None: ...
+    def from_env(self, name: str, default: Optional[Any] = None, required: bool = False, as_: Optional[_Callable[..., Any]] = None) -> None: ...
     def from_value(self, value: Any) -> None: ...
 
 
@@ -262,7 +262,7 @@ class Configuration(Object[Any]):
     def from_yaml(self, filepath: Union[Path, str], required: bool = False, loader: Optional[Any] = None, envs_required: bool = False) -> None: ...
     def from_pydantic(self, settings: PydanticSettings, required: bool = False, **kwargs: Any) -> None: ...
     def from_dict(self, options: _Dict[str, Any], required: bool = False) -> None: ...
-    def from_env(self, name: str, default: Optional[Any] = None, required: bool = False) -> None: ...
+    def from_env(self, name: str, default: Optional[Any] = None, required: bool = False, as_: Optional[_Callable[..., Any]] = None) -> None: ...
     def from_value(self, value: Any) -> None: ...
 
 

src/dependency_injector/providers.pyx

@@ -1689,7 +1689,7 @@ cdef class ConfigurationOption(Provider):
 
         self.override(merge_dicts(current_config, options))
 
-    def from_env(self, name, default=UNDEFINED, required=UNDEFINED):
+    def from_env(self, name, default=UNDEFINED, required=UNDEFINED, as_=UNDEFINED):
         """Load configuration value from the environment variable.
 
         :param name: Name of the environment variable.
@@ -1701,6 +1701,9 @@ cdef class ConfigurationOption(Provider):
         :param required: When required is True, raise an exception if environment variable is undefined.
         :type required: bool
 
+        :param as_: Callable used for type casting (int, float, etc).
+        :type as_: object
+
         :rtype: None
         """
         value = os.environ.get(name, default)
@@ -1711,6 +1714,9 @@ cdef class ConfigurationOption(Provider):
                 raise ValueError('Environment variable "{0}" is undefined'.format(name))
             value = None
 
+        if as_ is not UNDEFINED:
+            value = as_(value)
+
         self.override(value)
 
     def from_value(self, value):
@@ -2191,7 +2197,7 @@ cdef class Configuration(Object):
             current_config = {}
         self.override(merge_dicts(current_config, options))
 
-    def from_env(self, name, default=UNDEFINED, required=UNDEFINED):
+    def from_env(self, name, default=UNDEFINED, required=UNDEFINED, as_=UNDEFINED):
         """Load configuration value from the environment variable.
 
         :param name: Name of the environment variable.
@@ -2203,6 +2209,9 @@ cdef class Configuration(Object):
         :param required: When required is True, raise an exception if environment variable is undefined.
         :type required: bool
 
+        :param as_: Callable used for type casting (int, float, etc).
+        :type as_: object
+
         :rtype: None
         """
         value = os.environ.get(name, default)
@@ -2213,6 +2222,9 @@ cdef class Configuration(Object):
                 raise ValueError('Environment variable "{0}" is undefined'.format(name))
             value = None
 
+        if as_ is not UNDEFINED:
+            value = as_(value)
+
         self.override(value)
 
     def from_value(self, value):

tests/typing/configuration.py

@@ -14,7 +14,11 @@ config2.from_ini(Path("config.ini"))
 
 config2.from_yaml("config.yml")
 config2.from_yaml(Path("config.yml"))
+
 config2.from_env("ENV", "default")
+config2.from_env("ENV", as_=int, default=123)
+config2.from_env("ENV", as_=float, required=True)
+config2.from_env("ENV", as_=lambda env: str(env))
 
 # Test 3: to check as_*() methods
 config3 = providers.Configuration()

tests/unit/providers/configuration/conftest.py

@@ -106,7 +106,11 @@ def environment_variables():
     os.environ["CONFIG_TEST_ENV"] = "test-value"
     os.environ["CONFIG_TEST_PATH"] = "test-path"
     os.environ["DEFINED"] = "defined"
+    os.environ["EMPTY"] = ""
+    os.environ["CONFIG_INT"] = "42"
     yield
     os.environ.pop("CONFIG_TEST_ENV", None)
     os.environ.pop("CONFIG_TEST_PATH", None)
     os.environ.pop("DEFINED", None)
+    os.environ.pop("EMPTY", None)
+    os.environ.pop("CONFIG_INT", None)

tests/unit/providers/configuration/test_from_env_py2_py3.py

@@ -31,6 +31,54 @@ def test_option_default_none(config):
     assert config.option() is None
 
 
+def test_as_(config):
+    config.from_env("CONFIG_INT", as_=int)
+    assert config() == 42
+    assert isinstance(config(), int)
+
+
+def test_as__default(config):
+    config.from_env("UNDEFINED", as_=int, default="33")
+    assert config() == 33
+    assert isinstance(config(), int)
+
+
+def test_as__undefined_required(config):
+    with raises(ValueError):
+        config.from_env("UNDEFINED", as_=int, required=True)
+    assert config() == {}
+
+
+def test_as__defined_empty(config):
+    with raises(ValueError):
+        config.from_env("EMPTY", as_=int)
+    assert config() == {}
+
+
+def test_option_as_(config):
+    config.option.from_env("CONFIG_INT", as_=int)
+    assert config.option() == 42
+    assert isinstance(config.option(), int)
+
+
+def test_option_as__default(config):
+    config.option.from_env("UNDEFINED", as_=int, default="33")
+    assert config.option() == 33
+    assert isinstance(config.option(), int)
+
+
+def test_option_as__undefined_required(config):
+    with raises(ValueError):
+        config.option.from_env("UNDEFINED", as_=int, required=True)
+    assert config.option() is None
+
+
+def test_option_as__defined_empty(config):
+    with raises(ValueError):
+        config.option.from_env("EMPTY", as_=int)
+    assert config.option() is None
+
+
 @mark.parametrize("config_type", ["strict"])
 def test_undefined_in_strict_mode(config):
     with raises(ValueError):