import numpy as np
fd = open(filename , 'rb') #'r' for read, 'b' for binary
read_data = np.fromfile(fd, np.float32) #'float32' or one of the other numpy-datatypes
shape_xy = (270,207)
tau = read_data.reshape(shape_xy)
fd.close()

import numpy as np
from bz2 import *
fd = BZ2File(filename, 'r')
read_data = array(fromstring(fd.read(), np.dtype('f4'))) #fd.read() returns a string, fromstring converts to float32
shape_xy = (270,207)
tau = read_data.reshape(shape_xy)
fd.close()