Add interpolation of environment variables for Configuration provider

docs/main/changelog.rst

@@ -7,6 +7,11 @@ that were made in every particular version.
 From version 0.7.6 *Dependency Injector* framework strictly 
 follows `Semantic versioning`_
 
+3.18.1
+------
+- Add interpolation of environment variables to ``Configuration.from_yaml()`` and
+  ``Configuration.from_ini()``.
+
 3.18.0
 ------
 - Add ``Configuration.from_yaml()`` method to load configuration from the yaml file.

src/dependency_injector/__init__.py

@@ -1,6 +1,6 @@
 """Dependency injector top-level package."""
 
-__version__ = '3.18.0'
+__version__ = '3.18.1'
 """Version number that follows semantic versioning.
 
 :type: str

src/dependency_injector/providers.pyx

@@ -5,6 +5,7 @@ Powered by Cython.
 
 import copy
 import os
+import re
 import sys
 import types
 import threading
@@ -49,6 +50,29 @@ else:  # pragma: no cover
                                     copy.deepcopy(obj.im_self, memo),
                                     obj.im_class)
 
+if yaml:
+    yaml_env_marker_pattern = re.compile(r'\$\{([^}^{]+)\}')
+    def yaml_env_marker_constructor(_, node):
+        """"Replace environment variable marker with its value."""
+        return os.path.expandvars(node.value)
+
+    yaml.add_implicit_resolver('!path', yaml_env_marker_pattern)
+    yaml.add_constructor('!path', yaml_env_marker_constructor)
+
+if sys.version_info[0] == 3:
+    class EnvInterpolation(iniconfigparser.BasicInterpolation):
+        """Interpolation which expands environment variables in values."""
+
+        def before_get(self, parser, section, option, value, defaults):
+            value = super().before_get(parser, section, option, value, defaults)
+            return os.path.expandvars(value)
+
+    def get_ini_parser():
+        return iniconfigparser.ConfigParser(interpolation=EnvInterpolation())
+else:
+    def get_ini_parser():
+        return iniconfigparser.SafeConfigParser(os.environ)
+
 
 cdef class Provider(object):
     """Base provider class.
@@ -1178,7 +1202,7 @@ cdef class Configuration(Object):
 
         :rtype: None
         """
-        parser = iniconfigparser.ConfigParser()
+        parser = get_ini_parser()
         parser.read([filepath])
 
         config = {}

tests/unit/providers/test_configuration_py2_py3.py

@@ -324,6 +324,41 @@ class ConfigFromIniTests(unittest.TestCase):
         self.assertEqual(self.config.section3.value3(), '3')
 
 
+class ConfigFromIniWithEnvInterpolationTests(unittest.TestCase):
+
+    def setUp(self):
+        self.config = providers.Configuration(name='config')
+
+        os.environ['CONFIG_TEST_ENV'] = 'test-value'
+
+        _, self.config_file = tempfile.mkstemp()
+        with open(self.config_file, 'w') as config_file:
+            config_file.write(
+                '[section1]\n'
+                'value1=${CONFIG_TEST_ENV}\n'
+            )
+
+    def tearDown(self):
+        del self.config
+        del os.environ['CONFIG_TEST_ENV']
+        os.unlink(self.config_file)
+
+    def test_env_variable_interpolation(self):
+        self.config.from_ini(self.config_file)
+
+        self.assertEqual(
+            self.config(),
+            {
+                'section1': {
+                    'value1': 'test-value',
+                },
+            },
+        )
+        self.assertEqual(self.config.section1(), {'value1': 'test-value'})
+        self.assertEqual(self.config.section1.value1(), 'test-value')
+
+
+
 class ConfigFromYamlTests(unittest.TestCase):
 
     def setUp(self):
@@ -414,6 +449,41 @@ class ConfigFromYamlTests(unittest.TestCase):
         )
 
 
+class ConfigFromYamlWithEnvInterpolationTests(unittest.TestCase):
+
+    def setUp(self):
+        self.config = providers.Configuration(name='config')
+
+        os.environ['CONFIG_TEST_ENV'] = 'test-value'
+
+        _, self.config_file = tempfile.mkstemp()
+        with open(self.config_file, 'w') as config_file:
+            config_file.write(
+                'section1:\n'
+                '  value1: ${CONFIG_TEST_ENV}\n'
+            )
+
+    def tearDown(self):
+        del self.config
+        del os.environ['CONFIG_TEST_ENV']
+        os.unlink(self.config_file)
+
+    @unittest.skipIf(sys.version_info[:2] == (3, 4), 'PyYAML does not support Python 3.4')
+    def test_env_variable_interpolation(self):
+        self.config.from_yaml(self.config_file)
+
+        self.assertEqual(
+            self.config(),
+            {
+                'section1': {
+                    'value1': 'test-value',
+                },
+            },
+        )
+        self.assertEqual(self.config.section1(), {'value1': 'test-value'})
+        self.assertEqual(self.config.section1.value1(), 'test-value')
+
+
 class ConfigFromDict(unittest.TestCase):
 
     def setUp(self):