Unladen Swallow was an optimization branch of CPython, the reference implementation of the Python programming language, which incorporated a just-in-time compiler built using LLVM into CPython's virtual machine. Like many things regarding Python (and the name "Python" itself), "Unladen Swallow" is a Monty Python reference, specifically to the joke about the airspeed velocity of unladen swallows in Monty Python and the Holy Grail . The project's stated goals were to provide full compatibility with CPython specific code while quintupling its performance, and for the project to eventually be merged into CPython. [1] [2] Although it fell short of all its published goals, some Unladen Swallow code was added into the main Python implementation, such as improvements to the cPickle module. [3] [1]
Unladen Swallow was sponsored by Google, and the project owners, Thomas Wouters, Jeffrey Yasskin, and Collin Winter, were Google employees, though most project contributors were not. [4] Unladen Swallow was hosted on Google Code. [5]
In March 2010, a Python Enhancement Proposal (PEP) which proposed merging Unladen Swallow into a special py3k-jit branch of Python's official repository was accepted. [1] However, its implementation was made difficult by Unladen being based on Python 2.6, with which Python 3 broke compatibility, and the PEP was subsequently withdrawn. [6]
In July 2010, speculation began on whether the project was dead or dying since the 2009 Q4 milestone had not yet been released, [7] and the traffic on Unladen's mailing list had decreased from 500 messages in January 2010 to fewer than 10 in September 2010. [8] It had also been reported that Unladen had lost Google's funding, [9] and in November 2010, Collin announced that "Jeffrey and I have been pulled on to other projects of higher importance to Google". [10] By early 2011, it was clear that the project was stopped. [6]
A 2009 Q4 development branch was created in January 2010, [14] but was not advertised on the website, and its milestone was unmet. [15]