Fix the LazyCryptContext stays lazy after init

setup.py

@@ -29,6 +29,7 @@ extras_require = {
         'Jinja2>=2.3',
         'docutils>=0.10',
         'flexmock>=0.9.7',
+        'mock==2.0.0',
         'psycopg2>=2.5.1',
         'pytz>=2014.2',
         'python-dateutil>=2.2',

sqlalchemy_utils/types/password.py

@@ -130,11 +130,15 @@ class PasswordType(types.TypeDecorator, ScalarCoercible):
         # Construct the passlib crypt context.
         self.context = LazyCryptContext(**kwargs)
 
-        if max_length is None:
-            max_length = self.calculate_max_length()
+        self._max_length = max_length
 
-        # Set the length to the now-calculated max length.
-        self.length = max_length
+    @property
+    def length(self):
+        """Get column length."""
+        if self._max_length is None:
+            self._max_length = self.calculate_max_length()
+
+        return self._max_length
 
     def calculate_max_length(self):
         # Calculate the largest possible encoded password.

tests/types/test_password.py

@@ -1,3 +1,4 @@
+import mock
 import pytest
 import sqlalchemy as sa
 from sqlalchemy import inspect
@@ -217,3 +218,19 @@ class TestPasswordType(object):
         obj = User()
         obj.password = b'b'
         assert obj.password.hash.decode('utf8').startswith('$pbkdf2-sha256$')
+
+    @pytest.mark.parametrize('max_length', [1, 103])
+    def test_constant_length(self, max_length):
+        """
+        Test that constant max_length is applied.
+        """
+        typ = PasswordType(max_length=max_length)
+        assert typ.length == max_length
+
+    def test_context_is_lazy(self):
+        """
+        Make sure the init doesn't evaluate the lazy context.
+        """
+        onload = mock.Mock(return_value={})
+        PasswordType(onload=onload)
+        assert not onload.called