Added Consul repository

Requires a `python-consul`'s `consul.Consul` object during
initialization

Author: Rafael Sierra

decouple.py

@@ -115,6 +115,34 @@ def __getitem__(self, key):
         return self.parser.get(self.SECTION, key)
 
 
+class RepositoryConsul(RepositoryEmpty):
+    """
+    Retrieves options keys from a consul connection.
+    """
+    def __init__(self, consul, root=''):
+        """
+        consul: consul.Consul object
+        root: Where to look for keys (prepended to the actual key name)
+        """
+        self.consul = consul
+        self.root = root
+        self.data = {}
+
+    def __contains__(self, key):
+        idx, data = self.consul.kv.get('/'.join([self.root, key]))
+        if not data:
+            return False
+        else:
+            self.data[key] = data.get('Value', None)
+            return True
+
+    def __getitem__(self, key):
+        # Makes sure that the data is loaded
+        if key in self:
+            return self.data[key]
+        return None
+
+
 class RepositoryEnv(RepositoryEmpty):
     """
     Retrieves option keys from .env files with fall back to os.environ.

tests/test_consul.py

@@ -0,0 +1,51 @@
+# coding: utf-8
+import os
+import pytest
+
+from decouple import Config, RepositoryConsul, UndefinedValueError
+
+class FakeConsul(object):
+    """This class is a monkey patch to simulate consul.Consul.kv.get"""
+    def __init__(self, fake_data=None):
+        self.fake_data = fake_data or {}
+        class KV:
+            idx = 0
+            @classmethod
+            def get(cls, key):
+                cls.idx += 1
+                if key in self.fake_data:
+                    return cls.idx, {'Value': self.fake_data[key]}
+                return cls.idx, None
+        self.kv = KV()
+
+
+@pytest.fixture
+def consul():
+    c = FakeConsul()
+    c.fake_data['myapp/secret_key'] = 'some really secure secret key'
+    c.fake_data['myapp/debug'] = False
+    c.fake_data['staging/debug'] = True
+    c.fake_data['unaccessible'] = 'not be accessible if root is set to `myapp`'
+    return c
+
+
+@pytest.fixture
+def config(consul):
+    return Config(RepositoryConsul(consul, 'myapp'))
+
+
+def test_consul_undefined(config):
+    with pytest.raises(UndefinedValueError):
+        # `unaccessible` is defined in a scope that this consul repository
+        # has no access to
+        config('unaccessible')
+
+
+def test_consul_get_bool(config):
+    assert config('debug', cast=bool) is False
+
+
+def test_consul_basic(config):
+    os.environ['unaccessible'] = 'overwrite'
+    assert config('unaccessible') == 'overwrite'
+    del os.environ['unaccessible']