Python-сообщество

import array
def reverse_with_array(data):
    a = array.array("L", data)
    a.byteswap()
    return a.tostring()

from timeit import Timer
import os, array
data = os.urandom(1024*1024)
b2 = bytearray(data)
def rev():
    assert len(data) % 4 == 0, "Data length must be multiple of 4 but is %s" % len(data)
    l = []
    i = iter(data)
    for x in range(len(data) // 4):
        l1 = [i.next(), i.next(), i.next(), i.next()]
        l1.reverse() 
        l += l1
    return "".join(l)
def rev_fast():
    b = b2
    #assert len(b) % 4 == 0, "Data length must be multiple of 4 but is %s" % len(data)
    #b = bytearray(data)
    for x in xrange(0, len(data), 4):
        b[0+x], b[1+x], b[2+x], b[3+x] = b[3+x], b[2+x], b[1+x], b[0+x]
    return b
def reverse_with_array():
    a = array.array("L", data)
    a.byteswap()
    return a.tostring()
print "1:", Timer(rev).timeit(10)
print "2:", Timer(rev_fast).timeit(10)
print "3:", Timer(reverse_with_array).timeit(10)

1: 6.54667590434
2: 3.62785130512
3: 0.0526457971614

MB = 200
DATA = "12345678" * ((MB*1024*1024)/(4*2))

import os
import array
 
def load_byteswapped_data(file, type_code="L"):
    a = array.array(type_code)
    file_size = os.fstat(file.fileno()).st_size
    a.fromfile(file, file_size/a.itemsize)
    a.byteswap()
    return a.tostring()
 
def save_byteswapped_data(file, data, type_code="L"):
    a = array.array(type_code, data)
    a.byteswap()
    a.tofile(file)
  
with open('data.dat', 'rb') as f:
    bs_data = load_byteswapped_data(f)
# do something with byteswapped data
# ...
with open('data1.dat', 'wb') as f:
    save_byteswapped_data(f, bs_data)

def m1(data):
    return data[3::-1]+data[:3:-1]