How to get the 1st Principal Component by PCA using Python?

Question

I have a set of 2D vectors presented in a n*2 matrix form.

I wish to get the 1st principal component, i.e. the vector that indicates the direction with

Answer 1

PCA gives only 2d vecs from 2d data.

Look at the picture in Wikipedia PCA:
starting with a point cloud (dataMatrix) like that, and using matplotlib.mlab.PCA,
myPCA.Wt[0] is the first PC, the long one in the picture.