Blobstore API for Python 3

This page describes how to use the Blobstore API, one of the legacy bundled services, with the Python 3 runtime for the standard environment. Your app can access the bundled services through the App Engine services SDK for Python 3 .

Overview

Since webapp is not supported in Python 3, you need to make some minimal changes when migrating Blobstore handler code from Python 2 to Python 3. To use the Blobstore API for Python 3, keep in mind the following:

Blobstore handler classes are utility classes. This means that the handler classes are no longer webapp-based, and you cannot use the blobstore_handlers module provided by the webapp package ( google.appengine.ext.webapp ) or the webapp2.RequestHandler parameters in subclasses of these handlers.
All of the methods in Blobstore handler classes require the WSGI environ dictionary as an input parameter.

The following sections show how to use BlobstoreUploadHandler and BlobstoreDownloadHandler classes for Python 3 in a Flask app and a WSGI app that does not use a Python framework. You can compare the Python 3 examples with the Python 2 example code to learn more about code change differences.

Example: Flask app

In Python 3, the Blobstore handler classes are part of module google.appengine.ext.blobstore . For a Flask app, all calls made to methods in BlobstoreUploadHandler and BlobstoreDownloadHandler classes require the request.environ dictionary ( request being imported from the flask module).

Compare the code changes made from Python 2 (webapp2) to Python 3 (Flask). Notice how the Flask app uses the request.environ parameter in the methods get_uploads() and send_blob() :

Python 2 (webapp2)

  class 
  
 PhotoUploadHandler 
 ( 
 blobstore_handlers 
 . 
 BlobstoreUploadHandler 
 ): 
 def 
  
 post 
 ( 
 self 
 ): 
 upload 
 = 
 self 
 . 
 get_uploads 
 ()[ 
 0 
 ] 
 user_photo 
 = 
 UserPhoto 
 ( 
 user 
 = 
 users 
 . 
 get_current_user 
 () 
 . 
 user_id 
 (), 
 blob_key 
 = 
 upload 
 . 
 key 
 ()) 
 user_photo 
 . 
 put 
 () 
 self 
 . 
 redirect 
 ( 
 '/view_photo/ 
 %s 
 ' 
 % 
 upload 
 . 
 key 
 ()) 
 class 
  
 ViewPhotoHandler 
 ( 
 blobstore_handlers 
 . 
 BlobstoreDownloadHandler 
 ): 
 def 
  
 get 
 ( 
 self 
 , 
 photo_key 
 ): 
 if 
 not 
 blobstore 
 . 
 get 
 ( 
 photo_key 
 ): 
 self 
 . 
 error 
 ( 
 404 
 ) 
 else 
 : 
 self 
 . 
 send_blob 
 ( 
 photo_key 
 ) 
 app 
 = 
 webapp2 
 . 
 WSGIApplication 
 ([ 
 ( 
 '/' 
 , 
 PhotoUploadFormHandler 
 ), 
 ( 
 '/upload_photo' 
 , 
 PhotoUploadHandler 
 ), 
 ( 
 '/view_photo/([^/]+)?' 
 , 
 ViewPhotoHandler 
 ), 
 ], 
 debug 
 = 
 True 
 )

Python 3 (Flask)

  class 
  
 PhotoUploadHandler 
 ( 
 blobstore 
 . 
 BlobstoreUploadHandler 
 ): 
 def 
  
 post 
 ( 
 self 
 ): 
 upload 
 = 
 self 
 . 
 get_uploads 
 ( 
 request 
 . 
 environ 
 )[ 
 0 
 ] 
 photo 
 = 
 PhotoUpload 
 ( 
 blob_key 
 = 
 upload 
 . 
 key 
 ()) 
 photo 
 . 
 put 
 () 
 return 
 redirect 
 ( 
 "/view_photo/ 
 %s 
 " 
 % 
 upload 
 . 
 key 
 ()) 
 class 
  
 ViewPhotoHandler 
 ( 
 blobstore 
 . 
 BlobstoreDownloadHandler 
 ): 
 def 
  
 get 
 ( 
 self 
 , 
 photo_key 
 ): 
 if 
 not 
 blobstore 
 . 
 get 
 ( 
 photo_key 
 ): 
 return 
 "Photo key not found" 
 , 
 404 
 else 
 : 
 headers 
 = 
 self 
 . 
 send_blob 
 ( 
 request 
 . 
 environ 
 , 
 photo_key 
 ) 
 # Prevent Flask from setting a default content-type. 
 # GAE sets it to a guessed type if the header is not set. 
 headers 
 [ 
 "Content-Type" 
 ] 
 = 
 None 
 return 
 "" 
 , 
 headers 
 @app 
 . 
 route 
 ( 
 "/view_photo/<photo_key>" 
 ) 
 def 
  
 view_photo 
 ( 
 photo_key 
 ): 
  
 """View photo given a key.""" 
 return 
 ViewPhotoHandler 
 () 
 . 
 get 
 ( 
 photo_key 
 ) 
 @app 
 . 
 route 
 ( 
 "/upload_photo" 
 , 
 methods 
 = 
 [ 
 "POST" 
 ]) 
 def 
  
 upload_photo 
 (): 
  
 """Upload handler called by blobstore when a blob is uploaded in the test.""" 
 return 
 PhotoUploadHandler 
 () 
 . 
 post 
 ()

To view the complete code sample for Python 3 (Flask), see GitHub .

Example: WSGI app without a web framework

The following Python 3 (WSGI app) code shows how to add the environ parameter when using Blobstore handler classes for a WSGI app without a web framework. Notice how the environ parameter is used in the get_uploads() and send_blob() methods, and compare it with the Python 2 version:

Python 2

  class 
  
 PhotoUploadHandler 
 ( 
 blobstore_handlers 
 . 
 BlobstoreUploadHandler 
 ): 
 def 
  
 post 
 ( 
 self 
 ): 
 upload 
 = 
 self 
 . 
 get_uploads 
 ()[ 
 0 
 ] 
 user_photo 
 = 
 UserPhoto 
 ( 
 user 
 = 
 users 
 . 
 get_current_user 
 () 
 . 
 user_id 
 (), 
 blob_key 
 = 
 upload 
 . 
 key 
 ()) 
 user_photo 
 . 
 put 
 () 
 self 
 . 
 redirect 
 ( 
 '/view_photo/ 
 %s 
 ' 
 % 
 upload 
 . 
 key 
 ()) 
 class 
  
 ViewPhotoHandler 
 ( 
 blobstore_handlers 
 . 
 BlobstoreDownloadHandler 
 ): 
 def 
  
 get 
 ( 
 self 
 , 
 photo_key 
 ): 
 if 
 not 
 blobstore 
 . 
 get 
 ( 
 photo_key 
 ): 
 self 
 . 
 error 
 ( 
 404 
 ) 
 else 
 : 
 self 
 . 
 send_blob 
 ( 
 photo_key 
 ) 
 app 
 = 
 webapp2 
 . 
 WSGIApplication 
 ([ 
 ( 
 '/' 
 , 
 PhotoUploadFormHandler 
 ), 
 ( 
 '/upload_photo' 
 , 
 PhotoUploadHandler 
 ), 
 ( 
 '/view_photo/([^/]+)?' 
 , 
 ViewPhotoHandler 
 ), 
 ], 
 debug 
 = 
 True 
 )

Python 3

  class 
  
 UploadPhotoHandler 
 ( 
 blobstore 
 . 
 BlobstoreUploadHandler 
 ): 
  
 """Upload handler called by blobstore when a blob is uploaded in the test.""" 
 def 
  
 post 
 ( 
 self 
 , 
 environ 
 ): 
 upload 
 = 
 self 
 . 
 get_uploads 
 ( 
 environ 
 )[ 
 0 
 ] 
 user_photo 
 = 
 UserPhoto 
 ( 
 blob_key 
 = 
 upload 
 . 
 key 
 ()) 
 user_photo 
 . 
 put 
 () 
 # Redirect to the '/view_photo/<Photo Key>' URL 
 return 
 ( 
 "" 
 , 
 http 
 . 
 HTTPStatus 
 . 
 FOUND 
 , 
 [( 
 "Location" 
 , 
 "/view_photo/ 
 %s 
 " 
 % 
 upload 
 . 
 key 
 ())], 
 ) 
 class 
  
 ViewPhotoHandler 
 ( 
 blobstore 
 . 
 BlobstoreDownloadHandler 
 ): 
 def 
  
 get_photo 
 ( 
 self 
 , 
 environ 
 , 
 photo_key 
 ): 
 if 
 not 
 blobstore 
 . 
 get 
 ( 
 photo_key 
 ): 
 return 
 "Photo key not found" 
 , 
 http 
 . 
 HTTPStatus 
 . 
 NOT_FOUND 
 , 
 [] 
 else 
 : 
 return 
 ( 
 "" 
 , 
 http 
 . 
 HTTPStatus 
 . 
 OK 
 , 
 list 
 ( 
 self 
 . 
 send_blob 
 ( 
 environ 
 , 
 photo_key 
 ) 
 . 
 items 
 ()), 
 ) 
 def 
  
 get 
 ( 
 self 
 , 
 environ 
 ): 
 photo_key 
 = 
 ( 
 environ 
 [ 
 "app.url_args" 
 ])[ 
 0 
 ] 
 return 
 self 
 . 
 get_photo 
 ( 
 environ 
 , 
 photo_key 
 ) 
 # map urls to functions 
 urls 
 = 
 [ 
 ( 
 r 
 "^$" 
 , 
 UploadFormHandler 
 ), 
 ( 
 r 
 "upload_photo/?$" 
 , 
 UploadPhotoHandler 
 ), 
 ( 
 r 
 "view_photo/(.+)$" 
 , 
 ViewPhotoHandler 
 ), 
 ]

To view the complete code sample for Python 3, see GitHub .