django开发时：我的url.py的模式中是这样写的：
urlpatterns = patterns('',
                       (r'^time/$', current_datetime),
                       (r'^time/plus/(\d+)/$', hours_ahead),
                       (r'^search/$','mysite.books.views.search')
                       (r'^contact/$', 'mysite.books.views.contact')
而我在运行的时候，从网页登录，输入网址：http://127.0.0.1:8000/time/，却出现如下错误：

TypeError at /time/

'tuple' object is not callable

Request Method:	GET
Request URL:	http://127.0.0.1:8000/time/
Django Version:	1.4.1
Exception Type:	TypeError
Exception Value:	'tuple' object is not callable
Exception Location:	/home/liul/workspace/mysite/mysite/urls.py in , line 20
Python Executable:	/usr/bin/python2.7
Python Version:	2.7.3

经过验证，原来是url中所填写的函数变量search和contact与python内部模块中的函数重名了，就会出现这种错误，所以改变这两个函数名或删掉他们就OK啦