import antigravity

The antigravity module, referencing the XKCD comic mentioning Python, was added to Python 3 by Skip Montanaro. You can read more about it here, one of the first spottings that I know of: http://sciyoshi.com/blog/2008/dec/30/import-antigravity/).

But it really originated in Google App Engine! It was a last-minute addition when we launched App Engine on April 7, 2008. A few weeks before launch, when most code was already frozen, the App Engine team at Google decided we wanted an easter egg. After a great many suggestions, some too complex, some too obscure, some too risky, we chose the "antigravity" module. The App Engine version is a little more elaborate than the Python 3 version: it defines a fly() function while can randomly do one of two things: with a probability of 10%, it redirects to the XKCD comic; otherwise, it simply renders the text of the comic in HTML (with a link to the comic on the last line). To invoke it in your App Engine app, you'd have to write a little main program, like this:

import antigravity

def main():
    antigravity.fly()

if __name__ == '__main__':
    main()

Update: The Python 3 stdlib version has an easter egg inside the easter egg, if you inspect the source code: it defines a function that purports to implement the XKCD geohashing algorithm.