Added validator param support.

README.rst

@@ -167,6 +167,22 @@ An example of one might be returning a datastructure expected by a framework:
         'LOCATION': '127.0.0.1:6379:0', 'OPTIONS': {'PASSWORD': 'redispass'}}
 
 
+Value Validators
+~~~~~~~~~~~~~~~~
+Value validators are callables that are run on the environment variable after a
+preprocessor, type casting and postprocessor. If the return value of the validator
+is falsy, error will be raised.
+
+.. code-block:: python
+
+    import logging
+
+    to_upper = lambda v: v.upper()
+
+    env('LOG_LEVEL', preprocessor=to_upper, validator=lambda v: hasattr(logging, v))
+    env.int('PORT', validator=lambda v: v > 0 and v < 65535)
+
+
 Environment File
 ~~~~~~~~~~~~~~~~
 Read from a .env file (line delimited KEY=VALUE):
@@ -191,6 +207,7 @@ To run the tests install tox::
 
     pip install tox
 
-Then run them with::
+Then run them with:
 
     make test
+

envparse.py

@@ -16,7 +16,7 @@
     import urlparse
 
 
-__version__ = '0.2.0'
+__version__ = '0.3.0'
 
 
 logger = logging.getLogger(__file__)
@@ -57,7 +57,8 @@ def __init__(self, **schema):
         self.schema = schema
 
     def __call__(self, var, default=NOTSET, cast=None, subcast=None,
-                 force=False, preprocessor=None, postprocessor=None):
+                 force=False, preprocessor=None, postprocessor=None,
+                 validator=None):
         """
         Return value for given environment variable.
 
@@ -69,6 +70,8 @@ def __call__(self, var, default=NOTSET, cast=None, subcast=None,
         :param force: force to cast to type even if default is set.
         :param preprocessor: callable to run on pre-casted value.
         :param postprocessor: callable to run on casted value.
+        :param validator: callable which should return truthy value, otherwise
+                          ConfigurationError will be thrown.
 
         :returns: Value from environment or default (if set).
         """
@@ -111,6 +114,9 @@ def __call__(self, var, default=NOTSET, cast=None, subcast=None,
             value = self.cast(value, cast, subcast)
         if postprocessor:
             value = postprocessor(value)
+        if validator and not validator(value):
+            raise ConfigurationError("Value '{}' is invalid for variable '{}'"
+                                     .format(value, var))
         return value
 
     @classmethod

tests/test_casts.py

@@ -145,6 +145,15 @@ def django_redis(url):
                       postprocessor=django_redis))
 
 
+def test_validator():
+    env.int('INT', validator=lambda v: v in [41, 42])
+    env.json('JSON', validator=lambda v: 'foo' in v)
+    with pytest.raises(ConfigurationError):
+        env.int('INT', validator=lambda v: v in [1, 2])
+    with pytest.raises(ConfigurationError):
+        env.json('JSON', validator=lambda v: 'bar' in v)
+
+
 def test_schema():
     env = Env(STR=str, STR_DEFAULT=dict(cast=str, default='default'),
               INT=int, LIST_STR=list, LIST_INT=dict(cast=list, subcast=int))