Does Google App Engine allow creation of files and folders on the server?
You can read files from your own project - You cannot write to the file system
from the FAQ ...
Why can't I write to this file?
Writing to local files is not supported in App Engine due to the distributed nature of your application. Instead, data which must be persisted should be stored in the distributed datastore. For more information see the documentation on the runtime sandbox
An App Engine application cannot:
write to the filesystem. Applications must use the App Engine datastore for storing persistent data. Reading from the filesystem is allowed, and all application files uploaded with the application are available.
open a socket or access another host directly. An application can use the App Engine URL fetch service to make HTTP and HTTPS requests to other hosts on ports 80 and 443, respectively.
spawn a sub-process or thread. A web request to an application must be handled in a single process within a few seconds. Processes that take a very long time to respond are terminated to avoid overloading the web server.
make other kinds of system calls.
New information. Answer is Yes, but you have to use their cloud storage for write access. You can not use regular files for your purpose.
https://developers.google.com/appengine/docs/java/googlecloudstorageclient/
It also has Python API as well as RESTful API.