The Google Cloud SDK - part 003 .

The webapp2 is a lightweight Python web framework compatible with Google App Engine’s.
The webapp2 project, by Rodrigo Moraes, started as a fork of the App Engine web app framework.
The webapp2 includes a number of features such as improved support for URI routing, session management and localization.
You can see google documentation about this python module this link.
They say:
"webapp2 is compatible with the WSGI standard for Python web applications. You don't have to use webapp2 to write Python applications for App Engine. Other web application frameworks, such as Django, work with App Engine, and App Engine supports any Python code that uses the CGI standard. "
This is default start python example from Google Cloud SDK tested in the last tutorial.

import webapp2

class MainPage(webapp2.RequestHandler):
    def get(self):
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.write('Hello, World!')

app = webapp2.WSGIApplication([
    ('/', MainPage),
], debug=True)

Remember how to deploy your project to google:

C:\Python27>cd python-docs-samples\appengine\standard\hello_world

C:\Python27\python-docs-samples\appengine\standard\hello_world>gcloud app deploy app.yaml
Services to deploy:

descriptor:      [C:\Python27\python-docs-samples\appengine\standard\hello_world\app.yaml]
source:          [C:\Python27\python-docs-samples\appengine\standard\hello_world]
target project:  [xxxxxx]
target service:  [default]
target version:  [xxxxxxxxxxxxx]
target url:      [https://xxxxxx.appspot.com]


Do you want to continue (Y/n)?  y

Beginning deployment of service [default]...

Now I make some changes into main.py file to show you how easy is to use it.
This file: main.py is set into setting file app.yaml like the script: main.app.
Let's make some changes.

The default project is set with --promote true the result is: after a number of uploads you got this error:

ERROR: (gcloud.app.deploy) Error Response: [400] Your app may not have more than 15 versions.

Please delete one of the existing versions before trying to create a new version.
...

To fix go to App Engine - Versions with selected versions and press Delete button.
Then you can make the upload with the command :

gcloud app deploy app.yaml

Also, you can use this:

gcloud app deploy app.yaml --stop-previous-version

Some info about your project can be seen with this command:

gcloud config list

You can see the gcloud versions with:

gcloud version

I tested also with python version 3.6.4 :

C:\Python364\Scripts>pip install webapp2
Requirement already satisfied: webapp2 in c:\python364\lib\site-packages
      2 python-dateutil-2.7.0 setuptools-39.0.0