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This page describes how to use the Blobstore API, one of the legacy bundled services,
with thePython 3 runtimefor
the standard environment. Your app can access the bundled services
through theApp 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 theblobstore_handlersmodule provided by the webapp package
(google.appengine.ext.webapp) or thewebapp2.RequestHandlerparameters in
subclasses of these handlers.
All of the methods in Blobstore handler classes require theWSGIenvirondictionaryas an input parameter.
The following sections show how to useBlobstoreUploadHandlerandBlobstoreDownloadHandlerclasses 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 thePython 2 example codeto learn more about code change differences.
Example: Flask app
In Python 3, the Blobstore handler classes are part of modulegoogle.appengine.ext.blobstore.
For a Flask app, all calls made to methods inBlobstoreUploadHandlerandBlobstoreDownloadHandlerclasses require therequest.environdictionary
(requestbeing imported from theflaskmodule).
Compare the code changes made from Python 2 (webapp2) to Python 3 (Flask). Notice how the
Flask app uses therequest.environparameter in the methodsget_uploads()andsend_blob():
classPhotoUploadHandler(blobstore.BlobstoreUploadHandler):defpost(self):upload=self.get_uploads(request.environ)[0]photo=PhotoUpload(blob_key=upload.key())photo.put()returnredirect("/view_photo/%s"%upload.key())classViewPhotoHandler(blobstore.BlobstoreDownloadHandler):defget(self,photo_key):ifnotblobstore.get(photo_key):return"Photo key not found",404else: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"]=Nonereturn"",headers@app.route("/view_photo/<photo_key>")defview_photo(photo_key):"""View photo given a key."""returnViewPhotoHandler().get(photo_key)@app.route("/upload_photo",methods=["POST"])defupload_photo():"""Upload handler called by blobstore when a blob is uploaded in the test."""returnPhotoUploadHandler().post()
To view the complete code sample for Python 3 (Flask), seeGitHub.
Example: WSGI app without a web framework
The following Python 3 (WSGI app) code shows how to add theenvironparameter
when using Blobstore handler classes for a WSGI app without a web framework.
Notice how theenvironparameter is used in theget_uploads()andsend_blob()methods,
and compare it with the Python 2 version:
classUploadPhotoHandler(blobstore.BlobstoreUploadHandler):"""Upload handler called by blobstore when a blob is uploaded in the test."""defpost(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>' URLreturn("",http.HTTPStatus.FOUND,[("Location","/view_photo/%s"%upload.key())],)classViewPhotoHandler(blobstore.BlobstoreDownloadHandler):defget_photo(self,environ,photo_key):ifnotblobstore.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()),)defget(self,environ):photo_key=(environ["app.url_args"])[0]returnself.get_photo(environ,photo_key)# map urls to functionsurls=[(r"^$",UploadFormHandler),(r"upload_photo/?$",UploadPhotoHandler),(r"view_photo/(.+)$",ViewPhotoHandler),]
To view the complete code sample for Python 3, seeGitHub.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-09-04 UTC."],[[["\u003cp\u003eThis document details the use of the Blobstore API with the Python 3 runtime in the standard App Engine environment, accessible via the App Engine services SDK for Python 3.\u003c/p\u003e\n"],["\u003cp\u003eMigrating Blobstore handler code from Python 2 to Python 3 requires adjustments, as the handler classes are no longer webapp-based, meaning you can't use the \u003ccode\u003eblobstore_handlers\u003c/code\u003e module from the webapp package.\u003c/p\u003e\n"],["\u003cp\u003eIn Python 3, all methods within Blobstore handler classes necessitate the WSGI \u003ccode\u003eenviron\u003c/code\u003e dictionary as a mandatory input parameter, unlike in Python 2.\u003c/p\u003e\n"],["\u003cp\u003eThe examples provided illustrate how to use \u003ccode\u003eBlobstoreUploadHandler\u003c/code\u003e and \u003ccode\u003eBlobstoreDownloadHandler\u003c/code\u003e classes within both a Flask application and a WSGI application without a framework, highlighting the use of the \u003ccode\u003erequest.environ\u003c/code\u003e parameter.\u003c/p\u003e\n"],["\u003cp\u003eComplete Python 3 code samples for both Flask and WSGI app examples are available on GitHub, offering a detailed comparison with their Python 2 counterparts.\u003c/p\u003e\n"]]],[],null,["# Blobstore API for Python 3\n\n\u003cbr /\u003e\n\n\u003cbr /\u003e\n\n\nThis page describes how to use the Blobstore API, one of the legacy bundled services,\nwith the [Python 3 runtime](/appengine/docs/standard/python3) for\nthe standard environment. Your app can access the bundled services\nthrough the [**App Engine services SDK for Python 3**](https://github.com/GoogleCloudPlatform/appengine-python-standard).\n\nOverview\n--------\n\nSince webapp is not supported in Python 3, you need to make some minimal\nchanges when migrating Blobstore handler code from Python 2 to Python 3. To use\nthe Blobstore API for Python 3, keep in mind the following:\n\n- Blobstore handler classes are utility classes. This means that the handler\n classes are no longer webapp-based, and you cannot use the\n `blobstore_handlers` module provided by the webapp package\n (`google.appengine.ext.webapp`) or the `webapp2.RequestHandler` parameters in\n subclasses of these handlers.\n\n- All of the methods in Blobstore handler classes require the\n [WSGI `environ` dictionary](https://www.python.org/dev/peps/pep-0333/#environ-variables)\n as an input parameter.\n\nThe following sections show how to use `BlobstoreUploadHandler` and\n`BlobstoreDownloadHandler` classes for Python\n3 in a Flask app and a WSGI app that does not use a Python framework. You can\ncompare the Python 3 examples with the\n[Python 2 example code](/appengine/docs/legacy/standard/python/blobstore#Complete_sample_application)\nto learn more about code change differences.\n\nExample: Flask app\n------------------\n\nIn Python 3, the Blobstore handler classes are part of module\n[`google.appengine.ext.blobstore`](/appengine/docs/standard/python3/reference/services/bundled/google/appengine/ext/blobstore).\nFor a Flask app, all calls made to methods in `BlobstoreUploadHandler` and\n`BlobstoreDownloadHandler` classes require the `request.environ` dictionary\n(`request` being imported from the `flask` module).\n\nCompare the code changes made from Python 2 (webapp2) to Python 3 (Flask). Notice how the\nFlask app uses the `request.environ` parameter in the methods `get_uploads()` and\n`send_blob()`: \n\n### Python 2 (webapp2)\n\n class PhotoUploadHandler(blobstore_handlers.BlobstoreUploadHandler):\n def post(self):\n upload = self.get_uploads()[0]\n user_photo = UserPhoto(\n user=users.get_current_user().user_id(),\n blob_key=upload.key())\n user_photo.put()\n\n self.redirect('/view_photo/%s' % upload.key())\n\n class ViewPhotoHandler(blobstore_handlers.BlobstoreDownloadHandler):\n def get(self, photo_key):\n if not blobstore.get(photo_key):\n self.error(404)\n else:\n self.send_blob(photo_key)\n\n app = webapp2.WSGIApplication([\n ('/', PhotoUploadFormHandler),\n ('/upload_photo', PhotoUploadHandler),\n ('/view_photo/([^/]+)?', ViewPhotoHandler),\n ], debug=True)\n\n### Python 3 (Flask)\n\n class PhotoUploadHandler(blobstore.BlobstoreUploadHandler):\n def post(self):\n upload = self.get_uploads(request.environ)[0]\n photo = PhotoUpload(blob_key=upload.key())\n photo.put()\n\n return redirect(\"/view_photo/%s\" % upload.key())\n\n\n class ViewPhotoHandler(blobstore.BlobstoreDownloadHandler):\n def get(self, photo_key):\n if not blobstore.get(photo_key):\n return \"Photo key not found\", 404\n else:\n headers = self.send_blob(request.environ, photo_key)\n\n # Prevent Flask from setting a default content-type.\n # GAE sets it to a guessed type if the header is not set.\n headers[\"Content-Type\"] = None\n return \"\", headers\n\n\n @app.route(\"/view_photo/\u003cphoto_key\u003e\")\n def view_photo(photo_key):\n \"\"\"View photo given a key.\"\"\"\n return ViewPhotoHandler().get(photo_key)\n\n\n @app.route(\"/upload_photo\", methods=[\"POST\"])\n def upload_photo():\n \"\"\"Upload handler called by blobstore when a blob is uploaded in the test.\"\"\"\n return PhotoUploadHandler().post()\n\nTo view the complete code sample for Python 3 (Flask), see\n[GitHub](https://github.com/GoogleCloudPlatform/python-docs-samples/tree/main/appengine/standard_python3/bundled-services).\n\nExample: WSGI app without a web framework\n-----------------------------------------\n\nThe following Python 3 (WSGI app) code shows how to add the `environ` parameter\nwhen using Blobstore handler classes for a WSGI app without a web framework.\nNotice how the `environ` parameter is used in the `get_uploads()` and `send_blob()` methods,\nand compare it with the Python 2 version: \n\n### Python 2\n\n class PhotoUploadHandler(blobstore_handlers.BlobstoreUploadHandler):\n def post(self):\n upload = self.get_uploads()[0]\n user_photo = UserPhoto(\n user=users.get_current_user().user_id(),\n blob_key=upload.key())\n user_photo.put()\n\n self.redirect('/view_photo/%s' % upload.key())\n\n class ViewPhotoHandler(blobstore_handlers.BlobstoreDownloadHandler):\n def get(self, photo_key):\n if not blobstore.get(photo_key):\n self.error(404)\n else:\n self.send_blob(photo_key)\n\n app = webapp2.WSGIApplication([\n ('/', PhotoUploadFormHandler),\n ('/upload_photo', PhotoUploadHandler),\n ('/view_photo/([^/]+)?', ViewPhotoHandler),\n ], debug=True)\n\n### Python 3\n\n class UploadPhotoHandler(blobstore.BlobstoreUploadHandler):\n \"\"\"Upload handler called by blobstore when a blob is uploaded in the test.\"\"\"\n\n def post(self, environ):\n upload = self.get_uploads(environ)[0]\n user_photo = UserPhoto(blob_key=upload.key())\n user_photo.put()\n\n # Redirect to the '/view_photo/\u003cPhoto Key\u003e' URL\n return (\n \"\",\n http.HTTPStatus.FOUND,\n [(\"Location\", \"/view_photo/%s\" % upload.key())],\n )\n\n\n class ViewPhotoHandler(blobstore.BlobstoreDownloadHandler):\n def get_photo(self, environ, photo_key):\n if not blobstore.get(photo_key):\n return \"Photo key not found\", http.HTTPStatus.NOT_FOUND, []\n else:\n return (\n \"\",\n http.HTTPStatus.OK,\n list(self.send_blob(environ, photo_key).items()),\n )\n\n def get(self, environ):\n photo_key = (environ[\"app.url_args\"])[0]\n return self.get_photo(environ, photo_key)\n\n\n # map urls to functions\n urls = [\n (r\"^$\", UploadFormHandler),\n (r\"upload_photo/?$\", UploadPhotoHandler),\n (r\"view_photo/(.+)$\", ViewPhotoHandler),\n ]\n\nTo view the complete code sample for Python 3, see\n[GitHub](https://github.com/GoogleCloudPlatform/python-docs-samples/tree/main/appengine/standard_python3/bundled-services)."]]
