add metaclass samples

michaelliao · michaelliao · commit 32347c199cc1 · 2015-04-01T14:00:19.000+08:00
diff --git a/py3/oop_advance/create_class_on_the_fly.py b/py3/oop_advance/create_class_on_the_fly.py
@@ -0,0 +1,13 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+def fn(self, name='world'): # 先定义函数
+    print('Hello, %s.' % name)
+
+Hello = type('Hello', (object,), dict(hello=fn)) # 创建Hello class
+
+h = Hello()
+print('call h.hello():')
+h.hello()
+print('type(Hello) =', type(Hello))
+print('type(h) =', type(h))
diff --git a/py3/oop_advance/orm.py b/py3/oop_advance/orm.py
@@ -0,0 +1,77 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+' Simple ORM using metaclass '
+
+class Field(object):
+
+    def __init__(self, name, column_type):
+        self.name = name
+        self.column_type = column_type
+
+    def __str__(self):
+        return '<%s:%s>' % (self.__class__.__name__, self.name)
+
+class StringField(Field):
+
+    def __init__(self, name):
+        super(StringField, self).__init__(name, 'varchar(100)')
+
+class IntegerField(Field):
+
+    def __init__(self, name):
+        super(IntegerField, self).__init__(name, 'bigint')
+
+class ModelMetaclass(type):
+
+    def __new__(cls, name, bases, attrs):
+        if name=='Model':
+            return type.__new__(cls, name, bases, attrs)
+        print('Found model: %s' % name)
+        mappings = dict()
+        for k, v in attrs.items():
+            if isinstance(v, Field):
+                print('Found mapping: %s ==> %s' % (k, v))
+                mappings[k] = v
+        for k in mappings.keys():
+            attrs.pop(k)
+        attrs['__mappings__'] = mappings # 保存属性和列的映射关系
+        attrs['__table__'] = name # 假设表名和类名一致
+        return type.__new__(cls, name, bases, attrs)
+
+class Model(dict, metaclass=ModelMetaclass):
+
+    def __init__(self, **kw):
+        super(Model, self).__init__(**kw)
+
+    def __getattr__(self, key):
+        try:
+            return self[key]
+        except KeyError:
+            raise AttributeError(r"'Model' object has no attribute '%s'" % key)
+
+    def __setattr__(self, key, value):
+        self[key] = value
+
+    def save(self):
+        fields = []
+        params = []
+        args = []
+        for k, v in self.__mappings__.items():
+            fields.append(v.name)
+            params.append('?')
+            args.append(getattr(self, k, None))
+        sql = 'insert into %s (%s) values (%s)' % (self.__table__, ','.join(fields), ','.join(params))
+        print('SQL: %s' % sql)
+        print('ARGS: %s' % str(args))
+
+# testing code:
+
+class User(Model):
+    id = IntegerField('id')
+    name = StringField('username')
+    email = StringField('email')
+    password = StringField('password')
+
+u = User(id=12345, name='Michael', email='test@orm.org', password='my-pwd')
+u.save()
diff --git a/py3/oop_advance/use_metaclass.py b/py3/oop_advance/use_metaclass.py
@@ -0,0 +1,19 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+# metaclass是创建类，所以必须从`type`类型派生：
+class ListMetaclass(type):
+    def __new__(cls, name, bases, attrs):
+        attrs['add'] = lambda self, value: self.append(value)
+        return type.__new__(cls, name, bases, attrs)
+
+# 指示使用ListMetaclass来定制类
+class MyList(list, metaclass=ListMetaclass):
+    pass
+
+L = MyList()
+L.add(1)
+L.add(2)
+L.add(3)
+L.add('END')
+print(L)
