Rotate labels in python ggplot facet_grid()

Is it possible to rotate the labels resulting from faceting in Python's implementation of ggplot? Here is an example of what I have in mind:

import pandas as pd
from ggplot import *

df = pd.DataFrame({'id': [1,2,3,4], 
               'left' :  [1,2,3,4],
               'right' : [2,1,4,3],
               'b' : ['alfa','beta','alfa','beta'], 
               'c' : ['one', 'one', 'two', 'two']})

dfm = pd.melt(df, id_vars=['b','c'], value_vars=['left','right'])

print(dfm)

      b    c variable  value
0  alfa  one     left      1
1  beta  one     left      2
2  alfa  two     left      3
3  beta  two     left      4
4  alfa  one    right      2
5  beta  one    right      1
6  alfa  two    right      4
7  beta  two    right      3


ggplot(dfm, aes(x='variable', y='value')) + \
    geom_point() + \
    facet_grid('b','c') + \
    theme(strip_text_y = element_text(angle = 0))

resulting plot

I would like to have the labels alpha and beta rotated horizontally, but I don't know how to achieve this. Thank you in advance.