模拟函数和方法的实现

我们知道python的函数是描述符，unbound method和bound method都是instancemethod类型，是通过函数的__get__方法返回的。还有类方法classmethod也是instancemethod类型的。instancemethod用im_class，im_self和im_func保存了方法调用的相关信息。静态方法staticmethod其实返回的就是函数本身。知道了这些之后可以自己用python来做个这些函数或方法的实现。

# -*- coding:utf-8 -*- #

class FunWrap(object):
	u"""包装一个函数"""
	def __init__(self, func):
		self.func = func
	
	def __get__(self, obj, typ = None):
		return szhinstancemethod(typ, obj, self)
	
	def __call__(self, *args):
		return self.func(*args)
	
	def __getattr__(self, name):
		return getattr(self.func, name)
	
class szhinstancemethod(object):
	u"""模拟instancemethod"""
	def __init__(self, im_class, im_self, im_func):
		self.im_class = im_class
		self.im_self = im_self
		self.im_func = im_func
		
	def __call__(self, *args):
		if not self.im_self:
			raise TypeError, "unbound method " + self.im_funcw.func_name + \
					"() must be called with " + \
					(self.im_class.__name__ if self.im_class else '?') + " instance"
		return self.im_func(self.im_self, *args)
	
	def __repr__(self):
		if not self.im_self:
			return '<unbound method ' + (self.im_class.__name__ if self.im_class else '?') \
				+ "." + self.im_func.func_name + "> __szh"
		else:
			return '<bound method ' + (self.im_class.__name__ if self.im_class else '?') \
				+ "." + self.im_func.func_name + " of " + str(self.im_self) + "> __szh"
			
class szhclassmethod(object):
	u"""模拟classmethod"""
	def __init__(self, func):
		self.func = func
	
	def __get__(self, obj, typ = None):
		typ = typ or type(obj)
		return szhinstancemethod(type(typ), typ, self.func)
	
class szhstaticmethod(object):
	u"""模拟staticmethod"""
	def __init__(self, func):
		self.func = func
	
	def __get__(self, obj, typ = None):
		return self.func
			
if __name__ == '__main__':
	class A(object):
		@FunWrap
		def f(self):
			print 'test method ' + str(self)
		
		@szhclassmethod
		@FunWrap
		def clsf(cls):
			print 'test class method '  + str(cls)
			
		@szhstaticmethod
		@FunWrap
		def staf():
			print 'test static method'
			
		
	
	a = A()
	a1 = A()
	print u"实例a访问方法f",a.f
	print u"实例a1访问方法f",a1.f
	print u"类A访问方法f",A.f
	a.f()
	a1.f()
	print u"实例a访问类方法clasf",a.clsf
	print u"类A访问类方法clasf",A.clsf
	A.clsf()
	a.clsf()
	print u"实例a访问静态方法staf",a.staf
	print u"类A访问静态方法staf",A.staf
	a.staf()