Perform type validation on string var_type for benefit of default value

envs/__init__.py

@@ -32,7 +32,7 @@ def validate_boolean(value):
 
 class Env(object):
     valid_types = {
-        'string': None,
+        'string': str,
         'boolean': validate_boolean,
         'list': list,
         'tuple': tuple,
@@ -56,16 +56,20 @@ def __call__(self, key, default=None, var_type='string', allow_none=True):
             if not allow_none:
                 raise EnvsValueException('{}: Environment Variable Not Set'.format(key))
             return value
-        return self.validate_type(value, self.valid_types[var_type], key)
+        return self.validate_type(value, var_type, key)
 
-    def validate_type(self, value, klass, key):
-        if not klass:
-            return value
+    def validate_type(self, value, var_type, key):
+        klass = self.valid_types[var_type]
         if klass in (validate_boolean, Decimal):
             return klass(value)
         if isinstance(value, klass):
             return value
-        return klass(ast.literal_eval(value))
+        try:
+            return klass(ast.literal_eval(value))
+        except ValueError as e:
+            raise TypeError(
+                f'Could not resolve value ({value}) as var_type ({var_type}) for key {key}'
+            ) from e
 
 
 env = Env()

envs/tests.py

@@ -114,6 +114,16 @@ def test_defaults(self):
         self.assertEqual(env('HELLO', 'true', var_type='boolean'), True)
         self.assertEqual(env('HELLO', Decimal('3.14'), var_type='decimal'), Decimal('3.14'))
 
+    def test_defaults_type_mismatch(self):
+        # Setting a default int with an implicit var_type of string should fail
+        # (otherwise default type is different than overridden type and that
+        # can cause problems in client code)
+        with self.assertRaises(TypeError):
+            env('HELLO', 5)
+        # Setting a default int with an explicit var_type of not-int should fail
+        with self.assertRaises(TypeError):
+            env('HELLO', 5, var_type='dict')
+
     def test_without_defaults_allow_none(self):
         self.assertEqual(env('HELLO'), None)
         self.assertEqual(env('HELLO', var_type='integer'), None)
@@ -198,4 +208,3 @@ def test_list_envs():
 
 if __name__ == '__main__':
     unittest.main()
-