I briefly mentioned the Grail browser near the start of Chapter 10. Many of Python’s Internet tools date back to and reuse the work that went into Grail, a full-blown Internet web browser that:
Is written entirely in Python
Uses the Tkinter GUI API to implement its user interface and render pages
Downloads and runs Python/Tkinter scripts as client-side applets
As mentioned earlier, Grail was something of a proof-of-concept for using Python to code large-scale Internet applications. It implements all the usual Internet protocols and works much like common browsers such as Netscape and Internet Explorer. Grail pages are implemented with the Tk text widgets that we met in the GUI part of this book.
More interestingly, the Grail browser allows applets to be written in Python. Grail applets are simply bits of Python code that live on a server but are run on a client. If an HTML document references a Python class and file that live on a server machine, Grail automatically downloads the Python code over a socket and runs it on the client machine, passing it information about the browser’s user interface. The downloaded Python code may use the passed-in browser context information to customize the user interface, add new kinds of widgets to it, and perform arbitrary client-side processing on the local machine. Roughly speaking, Python applets in Grail serve the same purposes as Java applets in common Internet browsers: they perform client-side tasks that ...