from itertools import combinations

 import binascii

 import os

 def find_all(source,aim):

      start=

      while True:

           start=source.find(aim,start)

           if start==-:

                return

           yield start

           start +=len(aim)

 def repair(source,aim,filedes,num,crc):

      matchlist=list(find_all(source,'\x0a'))

      for subnet in combinations(matchlist,num):

           subnet=sorted(subnet)

           temp=''

           if(num==):

                temp=source[:subnet[]]+'\x0d\x0a'+source[subnet[]+:subnet[]]+'\x0d\x0a'+source[subnet[]+:subnet[]]+'\x0d\x0a'+source[subnet[]+:]

           if(num==):

                temp=source[:subnet[]]+'\x0d\x0a'+source[subnet[]+:subnet[]]+'\x0d\x0a'+source[subnet[]+:]

           if(num==):

                temp=source[:subnet[]]+'\x0d\x0a'+source[subnet[]+:]

           if "%08x" % (binascii.crc32(temp)&0xFFFFFFFF)==crc:

                filedes.write(temp)

                filedes.write(binascii.a2b_hex(crc))

                filedes.flush()

                print "success"

                break;

      print "fail"

 uncfile=open("corrupt_735acee15fa4f3be8ecd0c6bcf294fd4.png","rb")

 cocfile=open("correct.png","wb")

 #first write

 correct=uncfile.read(0x6d)

 cocfile.write(correct)

 cocfile.flush()

 correct=uncfile.read(0x4)#length

 cocfile.write(correct)

 cocfile.flush()

 uncorrect=uncfile.read(0x20000-0x1+0x4)

 crc=uncfile.read(0x4)

 crc=binascii.hexlify(crc)

 print crc

 repair(uncorrect,'\x0a',cocfile,,crc)#

 #second write

 correct=uncfile.read(0x4)#length

 cocfile.write(correct)

 cocfile.flush()

 uncorrect=uncfile.read(0x20000-0x3+0x4)

 crc=uncfile.read(0x4)

 crc=binascii.hexlify(crc)

 print crc

 repair(uncorrect,'\x0a',cocfile,,crc)#

 #third write

 correct=uncfile.read(0x4)#length

 cocfile.write(correct)

 cocfile.flush()

 uncorrect=uncfile.read(0x20000-0x1+0x4)

 crc=uncfile.read(0x4)

 crc=binascii.hexlify(crc)

 print crc

 repair(uncorrect,'\x0a',cocfile,,crc)#

 #fourth write

 correct=uncfile.read(0x4+0x4+0x20000+0x4)

 cocfile.write(correct)

 cocfile.flush()

 #fifth write

 correct=uncfile.read(0x4)#length

 cocfile.write(correct)

 cocfile.flush()

 uncorrect=uncfile.read(0x20000-0x3+0x4)

 crc=uncfile.read(0x4)

 crc=binascii.hexlify(crc)

 print crc

 repair(uncorrect,'\x0a',cocfile,,crc)#

 #6th

 correct=uncfile.read(0x4)#length

 cocfile.write(correct)

 cocfile.flush()

 uncorrect=uncfile.read(0x20000-0x1+0x4)

 crc=uncfile.read(0x4)

 crc=binascii.hexlify(crc)

 print crc

 repair(uncorrect,'\x0a',cocfile,,crc)#

 #7th

 correct=uncfile.read(0x4)

 cocfile.write(correct)

 cocfile.flush()

 uncorrect=uncfile.read(0x20000-0x2+0x4)

 crc=uncfile.read(0x4)

 crc=binascii.hexlify(crc)

 print crc

 repair(uncorrect,'\x0a',cocfile,,crc)#

 #8th

 correct=uncfile.read(0x4+0x4+0x20000+0x4)

 cocfile.write(correct)

 cocfile.flush()

 #9th

 correct=uncfile.read(0x4)

 cocfile.write(correct)

 cocfile.flush()

 uncorrect=uncfile.read(0x20000-0x1+0x4)

 crc=uncfile.read(0x4)

 crc=binascii.hexlify(crc)

 print crc

 repair(uncorrect,'\x0a',cocfile,,crc)#

 #10th

 correct=uncfile.read(0x4+0x4+0x216f)

 cocfile.write(correct)

 cocfile.flush()

 uncfile.close()

 cocfile.close()