Implemented lazy regex compiling in Field classes to improve 'import mongoengine' performance

tests/test_utils.py

@@ -0,0 +1,38 @@
+import unittest
+import re
+
+from mongoengine.base.utils import LazyRegexCompiler
+
+signal_output = []
+
+
+class LazyRegexCompilerTest(unittest.TestCase):
+
+    def test_lazy_regex_compiler_verify_laziness_of_descriptor(self):
+        class UserEmail(object):
+            EMAIL_REGEX = LazyRegexCompiler('@', flags=32)
+
+        descriptor = UserEmail.__dict__['EMAIL_REGEX']
+        self.assertIsNone(descriptor._compiled_regex)
+
+        regex = UserEmail.EMAIL_REGEX
+        self.assertEqual(regex, re.compile('@', flags=32))
+        self.assertEqual(regex.search('user@domain.com').group(), '@')
+
+        user_email = UserEmail()
+        self.assertIs(user_email.EMAIL_REGEX, UserEmail.EMAIL_REGEX)
+
+    def test_lazy_regex_compiler_verify_cannot_set_descriptor_on_instance(self):
+        class UserEmail(object):
+            EMAIL_REGEX = LazyRegexCompiler('@')
+
+        user_email = UserEmail()
+        with self.assertRaises(AttributeError):
+            user_email.EMAIL_REGEX = re.compile('@')
+
+    def test_lazy_regex_compiler_verify_can_override_class_attr(self):
+        class UserEmail(object):
+            EMAIL_REGEX = LazyRegexCompiler('@')
+
+        UserEmail.EMAIL_REGEX = re.compile('cookies')
+        self.assertEqual(UserEmail.EMAIL_REGEX.search('Cake & cookies').group(), 'cookies')