How to make a pandas crosstab with percentages?

From Pandas 0.18.1 onwards, there’s a normalize option:

In [1]: pd.crosstab(df.A,df.B, normalize="index")
Out[1]:

B              A           B           C
A           
one     0.333333    0.333333    0.333333
three   0.333333    0.333333    0.333333
two     0.333333    0.333333    0.333333

Where you can normalise across either all, index (rows), or columns.

More details are available in the documentation.