Add env var prefix support

README.md

@@ -57,6 +57,17 @@ If there's an environment variable with the same name as the given configuration
 
     # even if the default for 'SOMETHING' or the value in the config file is different from 'value'
 
+
+It's useful to use prefixes to make sure your project environment variables do not conflict with other projects's environment variables:
+
+    from derpconf.config import Config
+
+    Config.allow_environment_variables(prefix='MYAPP_')
+
+    # called program with MYAPP_SOMETHING=value myprogram.py
+    assert config.SOMETHING == "value"
+
+
 Reloading Configurations
 ------------------------
 

derpconf/config.py

@@ -32,6 +32,7 @@ class Config(object):
     class_aliases = defaultdict(list)
     class_aliased_items = {}
     _allow_environment_variables = False
+    _environment_variables_prefix = ''
 
     @classmethod
     def define(cls, key, value, description, group='General'):
@@ -57,8 +58,9 @@ def get_conf_file(cls, conf_name, lookup_paths):
         return None
 
     @classmethod
-    def allow_environment_variables(cls):
+    def allow_environment_variables(cls, prefix=''):
         cls._allow_environment_variables = True
+        cls._environment_variables_prefix = prefix
 
     @classmethod
     def load(cls, path, conf_name=None, lookup_paths=[], defaults={}):
@@ -171,11 +173,12 @@ def __setattr__(self, name, value):
             super(Config, self).__setattr__(name, value)
 
     def __getattribute__(self, name):
-        if name in ['allow_environment_variables']:
+        if name in ['allow_environment_variables', '_environment_variables_prefix']:
             return super(Config, self).__getattribute__(name)
 
         if self.allow_environment_variables:
-            value = os.environ.get(name, None)
+            prefix = self._environment_variables_prefix
+            value = os.environ.get(prefix + name, None)
             if value is not None:
                 return value
 

vows/config_vows.py

@@ -183,6 +183,18 @@ def topic(self):
             def should_be_equal_to_env(self, topic):
                 expect(topic).to_equal("baz")
 
+        class WhenPassingPrefix(Vows.Context):
+            def topic(self):
+                os.environ['MYPREFIX_SOME_CONFIGURATION'] = "test value"
+                config = Config()
+
+                Config.allow_environment_variables(prefix='MYPREFIX_')
+
+                return config.SOME_CONFIGURATION
+
+            def should_be_equal_to_env(self, topic):
+                expect(topic).to_equal("test value")
+
     class WhenReloading(Vows.Context):
         def topic(self):
             class SpecialConfig(Config):