pyo looked like the best option, but have not tested it.
change audio playback speed library open source - Google Search
SoundTouch Sound Processing Library
SoundTouch Sound Processing Library
c++ - Changing tempo (speed) of audio - Stack Overflow
Rubber Band Audio Time Stretcher Library
DIRAC Time Stretching & Pitch Shifting : The DSP Dimension
Audio time-scale/pitch modification - Wikipedia, the free encyclopedia
mixxx source code - Google Search
start [Mixxx Wiki]
getting_involved [Mixxx Wiki]
Mixxx - Download the Best Free MP3 DJ Mixing Software
Oscillicious - Delicious Audio Software for Musicians
Oscillicious - Slice Beats with BeatCleaver
JAMDECK - Organic Music Sketching Software for Windows and Mac
~mixxxdevelopers/mixxx/trunk : contents of mixxx/README at revision 3430
python audio - Google Search
PythonInMusic - Python Wiki
SndObj Library Homepage
pyo - Python digital signal processing module. - Google Project Hosting
Download : The DSP Dimension