jsborjesson · January 18, 2014 21:38 · Jan 18, 2014
diff --git a/descriptors.py b/descriptors.py
@@ -0,0 +1,111 @@
+import re
+from weakref import WeakKeyDictionary
+
+class AdvancedDescriptor(object):
+    """
+    Base class for descriptors, is hard to understand but works for most cases.
+    from https://www.youtube.com/watch?v=P92z7m-kZpc
+    """
+
+    def __init__(self, name=None):
+        self.name = self.mangle(name)
+
+
+    def __get__(self, instance, owner):
+        if instance is None:
+            raise AttributeError('Can only be accessed from instance')
+        if self.name not in instance.__dict__:
+            raise AttributeError
+        return instance.__dict__[self.name]
+
+
+    def __set__(self, instance, value):
+        if self.name == None: self.fetchattr(instance)
+        instance.__dict__[self.name] = value
+
+
+    def __delete__(self, instance):
+        del instance.__dict__[self.name]
+
+
+    def fetchattr(self, instance):
+        for attr in instance.__class__.__dict__:
+            if attr.startswith('__'): continue
+            obj = instance.__class__.__dict__[attr]
+            if obj == self:
+                self.name = self.mangle(attr)
+                break
+
+
+    def mangle(self, name):
+        """Mangle name to __name."""
+        if name != None:
+            if name.startswith('__'):
+                raise AttributeError('Name conflict')
+            elif name.startswith('_'):
+                return '_' + name
+            else:
+                return '__' + name
+        return name
+
+
+
+class ValidationDescriptor(object):
+    """Simple base descriptor with support for validation."""
+
+    def __init__(self, default=None):
+        self.default = default
+        self.data = WeakKeyDictionary()
+
+    def __get__(self, instance, owner):
+        return self.data.get(instance, self.default)
+
+    def __set__(self, instance, value):
+        self.data[instance] = self.validate(value)
+
+    def __delete__(self, instance):
+        del self.data[instance]
+
+    def validate(self, value):
+        """Can either raise an exception or return a valid value."""
+        raise NotImplementedError('You need to implement a validate method')
+
+
+
+
+class RegexValidator(ValidationDescriptor):
+    """Descriptor that validates a regex when set."""
+
+    def __init__(self, regex=None):
+        self.regex = re.compile(regex) if isinstance(regex, str) else regex
+        super(RegexValidator, self).__init__()
+
+    def validate(self, value):
+        if self.regex.match(value) != None:
+            return value
+        else:
+            raise TypeError('"{}" is not valid.'.format(value))
+
+
+class Person(object):
+
+    email = RegexValidator(r'^(\w*)@(\w*)\.(\w{3})$')
+
+    def __init__(self, name, email):
+        self.name = name
+        self.email = email
+
+    def __str__(self):
+        return '{}: {}'.format(self.name, self.email)
+
+
+# demo
+if __name__ == '__main__':
+
+    d = Person('Alice', '[email protected]')
+    print(d)
+    try:
+        p = Person('Wallace', 'notanemail.com')
+    except Exception as e:
+        print(e)
+