Merge pull request faif#203 from aliciawyy/master

add another implementation for lazy property

Author: faif

.gitignore

@@ -1,2 +1,3 @@
 __pycache__
 *.pyc
+.idea

creational/lazy_evaluation.py

@@ -37,18 +37,35 @@ def __get__(self, obj, type_):
         return val
 
 
+def lazy_property2(fn):
+    attr = '_lazy__' + fn.__name__
+
+    @property
+    def _lazy_property(self):
+        if not hasattr(self, attr):
+            setattr(self, attr, fn(self))
+        return getattr(self, attr)
+    return _lazy_property
+
+
 class Person(object):
 
     def __init__(self, name, occupation):
         self.name = name
         self.occupation = occupation
+        self.call_count2 = 0
 
     @lazy_property
     def relatives(self):
         # Get all relatives, let's assume that it costs much time.
         relatives = "Many relatives."
         return relatives
 
+    @lazy_property2
+    def parents(self):
+        self.call_count2 += 1
+        return "Father and mother"
+
 
 def main():
     Jhon = Person('Jhon', 'Coder')
@@ -58,6 +75,10 @@ def main():
     print(u"Jhon's relatives: {0}".format(Jhon.relatives))
     print(u"After we've accessed `relatives`:")
     print(Jhon.__dict__)
+    print(Jhon.parents)
+    print(Jhon.__dict__)
+    print(Jhon.parents)
+    print(Jhon.call_count2)
 
 
 if __name__ == '__main__':
@@ -66,7 +87,11 @@ def main():
 ### OUTPUT ###
 # Name: Jhon    Occupation: Coder
 # Before we access `relatives`:
-# {'name': 'Jhon', 'occupation': 'Coder'}
+# {'call_count2': 0, 'name': 'Jhon', 'occupation': 'Coder'}
 # Jhon's relatives: Many relatives.
 # After we've accessed `relatives`:
-# {'relatives': 'Many relatives.', 'name': 'Jhon', 'occupation': 'Coder'}
+# {'relatives': 'Many relatives.', 'call_count2': 0, 'name': 'Jhon', 'occupation': 'Coder'}
+# Father and mother
+# {'_lazy__parents': 'Father and mother', 'relatives': 'Many relatives.', 'call_count2': 1, 'name': 'Jhon', 'occupation': 'Coder'}
+# Father and mother
+# 1

tests/test_lazy.py

@@ -11,18 +11,27 @@ def setUp(self):
         self.John = Person('John', 'Coder')
 
     def test_innate_properties(self):
-        self.assertDictEqual({'name': 'John', 'occupation': 'Coder'},
-                             self.John.__dict__)
+        self.assertDictEqual(
+            {'name': 'John', 'occupation': 'Coder', 'call_count2': 0},
+            self.John.__dict__
+        )
 
     def test_relatives_not_in_properties(self):
         self.assertNotIn('relatives', self.John.__dict__)
 
     def test_extended_properties(self):
         print(u"John's relatives: {0}".format(self.John.relatives))
-        self.assertDictEqual({'name': 'John', 'occupation': 'Coder',
-                              'relatives': 'Many relatives.'},
-                             self.John.__dict__)
+        self.assertDictEqual(
+            {'name': 'John', 'occupation': 'Coder',
+             'relatives': 'Many relatives.', 'call_count2': 0},
+            self.John.__dict__
+        )
 
     def test_relatives_after_access(self):
         print(u"John's relatives: {0}".format(self.John.relatives))
         self.assertIn('relatives', self.John.__dict__)
+
+    def test_parents(self):
+        for _ in range(2):
+            self.assertEqual(self.John.parents, "Father and mother")
+        self.assertEqual(self.John.call_count2, 1)