Dear Jinfang,
I don't think that it is possible to call Python from within Matlab, but I am not a Matlab programmer.
On the other hand, I know that there are some wrappers to call Matlab code from within Python, such as
pymatlab. I have used this wrapper once to use Matlab code (that I got from someone else) inside my Python environment. Maybe you want to explore this option.
Anyways, even if there is a possibility to use Python from within Matlab, bob.bio.gmm might not be the best starting point. While bob.bio.gmm provides code to extract I-Vectors, it does so within the Biometrics framework. Maybe, it would be easier to interface with the toolbox, which implements I-Vectors directly, which would be bob.learn.em (AFAIK). You might want to have a look into the implementation inside bob.bio.gmm to see, which functions are called for I-Vector extraction.
If there is no direct interface between Matlab and Python, you are still not lost. You might perform the I-Vector extraction with Python, write the I-Vectors to an HDF5 file, and read HDF5 with Matlab.
Finally, the better option would be to drop Matlab and completely switch to Python. I am not sure if this is feasible, though.
Best regards
Manuel