详解Django中Request对象的相关用法
从Request对象中获取数据
我们在第三章讲述View的函数时已经介绍过HttpRequest对象了，但当时并没有讲太多。 让我们回忆下：每个view函数的第一个参数是一个HttpRequest对象，就像下面这个hello()函数:
from django.http import HttpResponse
def hello(request):
return HttpResponse("Hello world")
HttpRequest对象，比如上面代码里的request变量，会有一些有趣的、你必须让自己熟悉的属性和方法，以便知道能拿它们来做些什么。 在view函数的执行过程中，你可以用这些属性来获取当前request的一些信息（比如，你正在加载这个页面的用户是谁，或者用的是什么浏览器）。
URL相关信息
HttpRequest对象包含当前请求URL的一些信息：
在view函数里，要始终用这个属性或方法来得到URL，而不要手动输入。 这会使得代码更加灵活，以便在其它地方重用。 下面是一个简单的例子：
# BAD!
def current_url_view_bad(request):
return HttpResponse("Welcome to the page at /current/")
# GOOD
def current_url_view_good(request):
return HttpResponse("Welcome to the page at %s" % request.path)
有关request的其它信息
request.META 是一个Python字典，包含了所有本次HTTP请求的Header信息，比如用户IP地址和用户Agent（通常是浏览器的名称和版本号）。 注意，Header信息的完整列表取决于用户所发送的Header信息和服务器端设置的Header信息。 这个字典中几个常见的键值有：
- HTTP_REFERER，进站前链接网页，如果有的话。 （请注意，它是REFERRER的笔误。）
- HTTP_USER_AGENT，用户浏览器的user-agent字符串，如果有的话。 例如： "Mozilla/5.0 (X11; U; Linux i686; fr-FR; rv:1.8.1.17) Gecko/20080829 Firefox/2.0.0.17" .
- REMOTE_ADDR 客户端IP，如："12.345.67.89" 。(如果申请是经过代理服务器的话，那么它可能是以逗号分割的多个IP地址，如："12.345.67.89,23.456.78.90" 。)
注意，因为 request.META 是一个普通的Python字典，因此当你试图访问一个不存在的键时，会触发一个KeyError异常。 （HTTP header信息是由用户的浏览器所提交的、不应该给予信任的“额外”数据，因此你总是应该好好设计你的应用以便当一个特定的Header数据不存在时，给出一个优雅的回应。）你应该用 try/except 语句，或者用Python字典的 get() 方法来处理这些“可能不存在的键”：
# BAD!
def ua_display_bad(request):
ua = request.META['HTTP_USER_AGENT'] # Might raise KeyError!
return HttpResponse("Your browser is %s" % ua)
# GOOD (VERSION 1)
def ua_display_good1(request):
try:
ua = request.META['HTTP_USER_AGENT']
except KeyError:
ua = 'unknown'
return HttpResponse("Your browser is %s" % ua)
# GOOD (VERSION 2)
def ua_display_good2(request):
ua = request.META.get('HTTP_USER_AGENT', 'unknown')
return HttpResponse("Your browser is %s" % ua)
我们鼓励你动手写一个简单的view函数来显示 request.META 的所有数据，这样你就知道里面有什么了。 这个view函数可能是这样的：
def display_meta(request):
values = request.META.items()
values.sort()
html = []
for k, v in values:
html.append('<tr><td>%s</td><td>%s</td></tr>' % (k, v))
return HttpResponse('<table>%s</table>' % '\n'.join(html))
做为一个练习，看你自己能不能把上面这个view函数改用Django模板系统来实现，而不是上面这样来手动输入HTML代码。 也可以试着把前面提到的 request.path 方法或 HttpRequest 对象的其它方法加进去。
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