redundant read in patch/read_cb #4

...
def read_cb(opaque, pos, length, buff):
        print "pos:",pos," length:",length
        f.seek(pos)
        block = f.read(length)
....

import librsync, os, shutil
#create the datfiles only once
file_1='1mb_a.dat'
file_2='1mb_b.dat'
file_new='1mb_c.dat'

if (not os.path.exists(file_1)):
    rnd = open('/dev/random','rb')
    dst = open(file_1, 'wb')
    dst.seek(0)
    dst.write(rnd.read(1000000));
    dst.close()
    rnd.close()

if (not os.path.exists(file_2)):
    src = open(file_1,'rb')
    cnt = src.read()
    src.close()

    #make a change in the content of file_1
    cnt_a=bytearray(cnt)
    if (cnt_a[10] != 'A'):
        cnt_a[10] = 'A'
    else:
        cnt_a[10] = 'B'

    #and store the changed content as file_2
    dst = open(file_2, 'wb')
    dst.seek(0)
    dst.write(str(cnt_a))
    dst.close()

#now create the signature, delta
dst = open(file_1, 'rb')
src = open(file_2, 'rb')

synced = open(file_new, 'wb')
signature = librsync.signature(dst)
delta = librsync.delta(src, signature)

# Step 3: synchronize the files.
librsync.patch(dst, delta, synced)