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A Scenic Drive through the Django Request-Respo...
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PyCon 2014
April 12, 2014
Programming
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A Scenic Drive through the Django Request-Response Cycle by Dan Langer
PyCon 2014
April 12, 2014
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Transcript
THE DJANGO REQUEST-RESPONSE CYCLE A Scenic Drive Though Daniel Langer
daniel@langer.me @dlanger
DANIEL LANGER Je m’appelle Handmade in Toronto
THE DJANGO REQUEST-RESPONSE CYCLE A Scenic Drive Though
LOTS OF THESE Django has http://www.safetysign.com/images/catlog/product/large/J6014.png
CLIENT
THE REQUEST
THE REQUEST $ curl -v http://www.daniellanger.com/hello/mtl/
THE REQUEST $ curl -v http://www.daniellanger.com/hello/mtl/ > GET /hello/mtl/ HTTP/1.1
> Host: www.daniellanger.com > Accept: */*
http://www.google.com/about/datacenters/gallery/#/all/5 THE INTERNET http://www.google.com/about/datacenters/gallery/#/all/5
THE WEB SERVER http://bit.ly/1jPAhEC
INTERFACE? mod_python FastCGI CGI
WEB SERVER GATEWAY INTERFACE PEP 333 December 2007 Phillip Eby
WEB SERVER GATEWAY INTERFACE def simple_app(environ, start_response): response_headers = [('Content-type',
'text/plain')] start_response(‘200 OK’, response_headers) return ['Hello world!\n']
DJANGO SPEAKS WSGI class WSGIHandler(base.BaseHandler): def __call__(self, environ, start_response): [...]
response = self.get_response(request) [...] start_response(status, response_headers) return response
DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware
4. View 5. Response middleware * Exception middleware (maybe)
MIDDLEWARE? A small digression
MIDDLEWARE A small digression “[A] light, low-level ‘plugin’ system for
globally altering Django’s input or output.” - https://docs.djangoproject.com/en/dev/topics/http/middleware/
MIDDLEWARE A small digression MIDDLEWARE_CLASSES = ( 'django.middleware.common.CommonMiddleware', 'django.middleware.csrf.CsrfViewMiddleware', [...]
)
DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware
4. View 5. Response middleware * Exception middleware (maybe)
REQUEST MIDDLEWARE class PyConRequestMiddleware(object): def process_request(self, request): return None #
or HttpResponse
BREAK TIME http://bit.ly/1mNlxWE
CLIENT WEB SERVER WSGI REQUEST Middleware
DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware
4. View 5. Response middleware * Exception middleware (maybe)
DJANGO.CORE.URLRESOLVERS http://www.daniellanger.com/hello/mtl/
DJANGO.CORE.URLRESOLVERS http://www.daniellanger.com/hello/mtl/ urlpatterns = patterns('' url(r'^hello/mtl/$', HiMtlView, name=‘hi__mtl’), url(r'^hello/(?P<city>\w+)/$', HiCityView,
name=‘hi_city’), )
DJANGO.CORE.URLRESOLVERS http://www.daniellanger.com/hello/mtl/ urlpatterns = patterns('' url(r'^hello/(?P<city>\w+)/$', HiCityView, name=‘hi_city’), url(r'^hello/mtl/$', HiMtlView,
name=‘hi__mtl’), ]
DJANGO.CORE.URLRESOLVERS urlpatterns = patterns('' url(r'^hello/(?P<city>\w+)/$', HiCityView, name=‘hi_city’), ) {% url
‘hi_city’ city=ottawa %} reverse(‘hi_city’, kwargs={‘city’: ‘ottawa’}) # Both return http://www.daniellanger.com/hello/ottawa/
DJANGO.CORE.URLRESOLVERS urlpatterns = patterns('' url(r'^cdn_hi/(?P<city>\w+)/$', HiCityView, name=‘hi_city’), ) {% url
‘hi_city’ city=ottawa %} reverse(‘hi_city’, kwargs={‘city’: ‘ottawa’}) # Both return http://www.daniellanger.com/cdn_hi/ottawa/
DJANGO.CORE.URLRESOLVERS http://www.daniellanger.com/hello/mtl/ urlpatterns = patterns('' url(r'^hello/mtl/$', HiMtlView, name=‘hi__mtl’), url(r'^hello/(?P<city>\w+)/$', HiCityView,
name=‘hi_city’), )
DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware
4. View 5. Response middleware * Exception middleware (maybe)
DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware
4. View 5. Response middleware * Exception middleware (maybe)
VIEWS def HiMtlView(request): html = “Bonjour <b>Mtl</b>!” return HttpResponse(html)
RESPONSES? HttpResponse HttpResponseRedirect JsonResponse StreamingHttpResponse
VIEWS def HiMtlView(request): html = “Bonjour <b>Mtl</b>!” return HttpResponse(html)
CLASS-BASED VIEWS from django.views.generic import View class HiMtlView(View): def get(self,
request): html = “Bonjour <b>Mtl</b>!” return HttpResponse(html)
TEMPLATES IN VIEWS from django.shortcuts import render def HiMtlView(request): context
= {‘city’: ‘Montreal’} return render(request, ‘hello.html’, context) # hello.html Bonjour <b>{{ city }}</b>!
TEMPLATES IN VIEWS def HiMtlView(request): context = {‘city’: ‘Montreal’} return
render(request, ‘hello.html’, context) # hello.html Bonjour <b>{{ city }}</b> (from {{ request_city }}!)
TEMPLATES IN VIEWS def HiMtlView(request): context = { ‘city’: ‘Montreal’,
‘request_city’: GeoIP.get_city(request)} return render(request, ‘hello.html’, context) # hello.html Bonjour <b>{{ city }}</b> (from {{ request_city }}!)
CONTEXT PROCESSORS def HiMtlView(request): context = { ‘city’: ‘Montreal’, ‘request_city’:
GeoIP.get_city(request)} return render(request, ‘hello.html’, context) # hello.html Bonjour <b>{{ city }}</b> (from {{ request_city }}!)
CONTEXT PROCESSORS def request_city(request) return { ‘request_city’: GeoIP.get_city(request), }
CONTEXT PROCESSORS def HiMtlView(request): context = {‘city’: ‘Montreal’} return render(request,
‘hello.html’, context) # hello.html Bonjour <b>{{ city }}</b> (from {{ request_city }}!)
The Doe Corporation presents PAUSE PAUSE- CAFE http://www.roadfood.com/photos/20865.jpg
CLIENT WEB SERVER WSGI URL RESOLUTION VIEW REQUEST Middleware VIEW
Middleware
DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware
4. View 5. Response middleware * Exception middleware (maybe)
RESPONSE MIDDLEWARE class PyConResponseMiddleware(object): def process_response(self, request, response): return None
# or HttpResponse
MIDDLEWARE class PyConMiddleware(object): def process_request(self, request): return None # or
HttpResponse def process_response(self, request, response): return response # or new HttpResponse
MIDDLEWARE MIDDLEWARE_CLASSES = ( 'django.middleware.common.CommonMiddleware', 'django.middleware.csrf.CsrfViewMiddleware', 'PyConMiddleware', [...] )
DJANGO.CORE.HANDLERS.BASEHANDLER 1. Request middleware 2. Resolve request.path_info 3. View middleware
4. View 5. Response middleware * Exception middleware (maybe)
EXCEPTION MIDDLEWARE class PyConMiddleware(object): def process_exception(self, request, exception): return None
# or HttpResponse
WEB SERVER GATEWAY INTERFACE class WSGIHandler(base.BaseHandler): def __call__(self, environ, start_response):
[...] response = self.get_response(request) [...] start_response(status, response_headers) return response
THE RESPONSE $ curl -v http://www.daniellanger.com/hello/mtl/ > GET /hello/mtl/ HTTP/1.1
> Host: www.daniellanger.com > Accept: */* < HTTP/1.1 200 OK < Server: nginx < Content-Type: text/html;charset=UTF-8 < Content-Length: 33 Bonjour Montreal! (from Toronto)
CLIENT WEB SERVER WSGI URL RESOLUTION VIEW WSGI WEB SERVER
CLIENT REQUEST Middleware RESPONSE Middleware VIEW Middleware EXCEPTION Middleware
@dlanger