Raise KeyError when key is not found in ini repositories

Enables RepositoryIni to be used in a collections.ChainMap
to allow cascading multiple repositories.

See #142

decouple.py

@@ -11,10 +11,10 @@
 
 
 if PYVERSION >= (3, 0, 0):
-    from configparser import ConfigParser
+    from configparser import ConfigParser, NoOptionError
     text_type = str
 else:
-    from ConfigParser import SafeConfigParser as ConfigParser
+    from ConfigParser import SafeConfigParser as ConfigParser, NoOptionError
     text_type = unicode
 
 if PYVERSION >= (3, 2, 0):
@@ -134,7 +134,10 @@ def __contains__(self, key):
                 self.parser.has_option(self.SECTION, key))
 
     def __getitem__(self, key):
-        return self.parser.get(self.SECTION, key)
+        try:
+            return self.parser.get(self.SECTION, key)
+        except NoOptionError:
+            raise KeyError(key)
 
 
 class RepositoryEnv(RepositoryEmpty):

tests/test_env.py

@@ -136,3 +136,7 @@ def test_env_with_quote(config):
     assert '"Y"' == config('KeyHasTwoDoubleQuote')
     assert '''"Y\'''' == config('KeyHasMixedQuotesAsData1')
     assert '''\'Y"''' == config('KeyHasMixedQuotesAsData2')
+
+def test_env_repo_keyerror(config):
+    with pytest.raises(KeyError):
+        config.repository['UndefinedKey']

tests/test_ini.py

@@ -121,3 +121,8 @@ def test_ini_undefined_but_present_in_os_environ(config):
 
 def test_ini_empty_string_means_false(config):
     assert False is config('KeyEmpty', cast=bool)
+
+
+def test_ini_repo_keyerror(config):
+    with pytest.raises(KeyError):
+        config.repository['UndefinedKey']

tests/test_secrets.py

@@ -1,5 +1,6 @@
 # coding: utf-8
 import os
+import pytest
 
 from decouple import Config, RepositorySecret
 
@@ -28,3 +29,10 @@ def test_secret_overriden_by_environ():
     os.environ['db_user'] = 'hi'
     assert 'hi' == config('db_user')
     del os.environ['db_user']
+
+def test_secret_repo_keyerror():
+    path = os.path.join(os.path.dirname(__file__), 'secrets')
+    repo = RepositorySecret(path)
+
+    with pytest.raises(KeyError):
+        repo['UndefinedKey']