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Before you can run your app in the Python 3 runtime of the App Engine standard environment, you may need to change some of the configuration files that App Engine uses:
app.yaml
. This file contains information about your app's code, such as the runtime and the app handlers.
appengine_config.py
. The Python 2 runtime uses this file to access third-party libraries and provide values for constants and "hook functions". The Python 3 runtime doesn't use this file.
app.yaml
The behavior of some fields in your app.yaml
configuration file has been modified. Remove any fields that are no longer supported and update other fields as described in the following table.
true
if you want to access the legacy bundled services for Python 3. api_version
entrypoint
configuring 1 thread per worker.
For example, when using the F4 instance class:
entrypoint: gunicorn -b :$PORT -w 8 --threads 1 main:app
See entrypoint best practices for recommended number of workers for each instance class.
libraries No longer supported Use therequirements.txt
file to declare dependencies and install client libraries. handlers: login Supported if app_engine_apis
is true
If you are not using the legacy bundled services for Python 3, use Identity and Access Management (IAM) for user management. handlers: script Modified In the Python 2 runtime, you use the script
field to route incoming requests to your app's script.
In the Python 3 runtime, you are required to use a web framework with in-app routing (such as Flask or Django) instead of using the script
field.
To migrate your app.yaml
file to the Python 3 runtime, do one of the following, depending on whether the file contains static handlers as well as script handlers:
app.yaml
file contains static handlers, do one of the following to ensure that requests for dynamic content are routed to your app's script:
script
fields. Then add an entrypoint
field to start a web server that runs your app. Requests that don't match any of your static handers will be directed to the web server you specified in the entrypoint
field. The web server and your app's web framework are responsible for routing the request to the correct script.script
fields with auto
. App Engine will automatically run your app in a web server (assuming your app meets a few requirements), and all requests that match a script handler will be directed to the web server. The web server and your app's web framework are responsible for routing the request to the correct script.app.yaml
file does not contain static handlers, remove all script
fields. All requests to your app will be directed to your app's web server, and your app's framework will route the request to the correct script. You can optionally add an entrypoint
field to customize the default startup behavior. If your app.yaml
has both types of handlers, you can still remove all the script handlers that would be marked auto
, leaving behind the static handlers as well as auto
handlers requiring other directives, such as the admin-only handler in the example below.Static file handling remains unchanged.
If you use any of the deprecated fields, App Engine returns an error when you deploy your app.
You can use the following examples to compare the differences between the app.yaml
files:
runtime: python27 api_version: 1 threadsafe: true handlers: - url: / script: home.app - url: /index\.html script: home.app - url: /stylesheets static_dir: stylesheets - url: /(.*\.(gif|png|jpg))$ static_files: static/\1 upload: static/.*\.(gif|png|jpg)$ - url: /admin/.* script: admin.app login: admin - url: /.* script: not_found.appPython 3
runtime: python313
app_engine_apis: true
handlers:
- url: /stylesheets
static_dir: stylesheets
- url: /(.*\.(gif|png|jpg))$
static_files: static/\1
upload: static/.*\.(gif|png|jpg)$
- url: /admin/.*
script: auto
login: admin
Note: For Python 3 the preferred WSGI-compatible web server is gunicorn
. When you use the optional entrypoint
field in your app.yaml
configuration file, the timeout for gunicorn
defaults to 30 seconds. To set a custom timeout, update the entrypoint
field: for example, entrypoint: gunicorn -b :$PORT --timeout=600
. In this case, make sure you have included gunicorn
in your requirements.txt
file. Removing appengine_config.py
The Python 2 runtime in the App Engine standard environment uses the appengine_config.py
file.
This file is ignored in the Python 3 runtime. Instead, the Python 3 runtime uses the standard requirements.txt
file to install dependencies, including dependencies that use native code.
Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.
Last updated 2025-08-07 UTC.
[[["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 2025-08-07 UTC."],[[["The Python 3 runtime on App Engine standard environment requires updates to the `app.yaml` file, while the `appengine_config.py` file is no longer used."],["Several fields in the `app.yaml` file are no longer supported in Python 3, including `api_version`, `application_readable`, `builtins`, `threadsafe`, and `libraries`, each having different changes in requirements or methodology."],["If using the legacy bundled services, the `app_engine_apis` field in `app.yaml` must be set to `true`, and it enables the use of `handlers: login`; otherwise, Identity and Access Management (IAM) should be used."],["In Python 3, the `script` field in `app.yaml` handlers is replaced by in-app routing using a web framework like Flask or Django, and the `entrypoint` field is used to start the web server, which will handle the routing."],["In the Python 3 runtime, dependencies are installed using the standard `requirements.txt` file instead of the `appengine_config.py` file used in Python 2, meaning the latter file can be removed."]]],[]]
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