Django REST Framework - POST slowness when body size greater than 1024 characters

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  As the title states.

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  l27.0.0.1:8000/api/users/1/
  

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  urls.py

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  ]
  
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  views.py

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  I want to have a 'post' model in Django that contains both images and text in the body of the post, but I am not sure how I should go about it.

  On the frontend React side, I'd like to have a content input form (along with title, etc.) that would allow users to type the text they want, and then insert photos to upload at any spot they choose in the text.

  On the backend Django side, I'd like the images to go to s3, but that seems like an issue I can work out once the actual uploading POSTing to the db is functional.

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• RestFul API endpoints with Django Rest Framework Class based views

  I have the following 4 class based views in DRF to perform CRUD operation on a model called Trips.

  from rest_framework import generics
  
  class TripCreateView(CreateAPIView): 
      #code that creates a Trip
  
  class TripListView(ListAPIView):
      #code that lists Trips
  
  class TripDetailView(RetrieveAPIView):
      #code that gives details of a Trip
  
  class TripUpdateView(UpdateAPIView):
      #code that updates a particular trip details
  
  class TripDeleteView(DestroyAPIView):
      #code that deletes an instance
  

  Now in-order to wire up the urls to each view, my urls.py looks like this:

  urlpatterns = [
  url(r'^trip/$', TripCreateView.as_view()),
  url(r'^trip/list/$',TripListView.as_view()),
  url(r'^trip/(?P<pk>[0-9]+)/detail/$', TripDetailView.as_view()),
  url(r'^trip/(?P<pk>[0-9]+)/update/$', TripUpdateView.as_view()),
  url(r'^trip/(?P<pk>[0-9]+)/delete/$', TripDeleteView.as_view())
  ]
  

  This works as expected.However, as is evident, those API endpoints are poorly designed since the URI has the http method as well in it. RESTFUL API endpoints don't have the HTTP method in the URI as look like this:

  Endpoint             HTTP METHOD          Result
  trips                GET                Gets all Trips
  trips/:id            GET                Gets details of a Trip
  trips                POST               Creates a Trip
  trips/:id            PUT                Updates a Trip
  trips:/id            DELETE             Deletes a Trip
  

  I know Viewsets can help achieve this but I can't use them because of certain other restrictions.Can this be achieved just by using class based views that I am using ?
• Why are Python operations 30× slower after calling time.sleep or subprocess.Popen?

  Consider the following loop:

  for i in range(20):
      if i == 10:
          subprocess.Popen(["echo"]) # command 1
      t_start = time.time()
      1+1 # command 2
      t_stop = time.time()
      print(t_stop - t_start)
  

  “command 2” command takes systematically longer to run when “command 1” is run before it. The following plot shows the execution time of 1+1 as a function of the loop index i, averaged over 100 runs.

  Execution of 1+1 is 30 times slower when preceded by subprocess.Popen.

  

  ---

  It gets even weirder. One may think that only the first command run after subprocess.Popen() is affected, but it is not the case. The following loop shows that all commands in the current loop iteration are affected. But the subsequent loops iterations seem to be mostly OK.

  var = 0
  for i in range(20):
      if i == 10:
        # command 1
        subprocess.Popen(['echo'])
      # command 2a
      t_start = time.time()
      1 + 1
      t_stop = time.time()
      print(t_stop - t_start)
      # command 2b
      t_start = time.time()
      print(1)
      t_stop = time.time()
      print(t_stop - t_start)
      # command 2c
      t_start = time.time()
      var += 1
      t_stop = time.time()
      print(t_stop - t_start)
  

  Here’s a plot of the execution times for this loop, average over 100 runs:

  

  ---

  More remarks:

  • We get the same effect when replacing subprocess.Popen() (“command 1”) with time.sleep(), or rawkit’s libraw C++ bindings initialization (libraw.bindings.LibRaw()). However, using other libraries with C++ bindings such as libraw.py, or OpenCV’s cv2.warpAffine() do not affect execution times. Opening files don’t either.
  • The effect is not caused by time.time(), because it is visible with timeit.timeit(), and even by measuring manually when print() result appear.
  • It also happens without a for-loop.
  • This happens even when a lot of different (possibly CPU- and memory-consuming) operations are performed between “command 1” (subprocess.Popen) and “command 2”.
  • With Numpy arrays, the slowdown appears to be proportional to the size of the array. With relatively big arrays (~ 60 M points), a simple arr += 1 operation can take up to 300 ms!

  ---

  Question: What may cause this effect, and why does it affect only the current loop iteration?

  I suspect that it could be related to context switching, but this doesn’t seem to explain why a whole loop iteration would affected. If context switching is indeed the cause, why do some commands trigger it while others don’t?
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  I found that the first one is twice slower than the second even if I run *.py scripts not via Visual Studio shell but directly from command line using python.exe:

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  C:\ProgramData\Anaconda3\python.exe  example.py     ---> **5.1 sec**
  

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