binary reverse data in python

Question

I wrote some code to binary reverse data in python. See below:

#!/usr/bin/python
import sys

data = sys.stdin.read()
for i in reversed(data):
    sys.stdout.write(chr(int('{:08b}'.format(ord(i))[::-1], 2)))

The program works fine!

$ echo -e 'hallo\c' | xxd -b 
00000000: 01101000 01100001 01101100 01101100 01101111           hallo

$ echo -e 'hallo\c' | ./stdi.py  | xxd -b 
00000000: 11110110 00110110 00110110 10000110 00010110           .66..

But the performance is poor.

$ time dd if=/dev/urandom count=1 bs=1M  | ./stdi.py > nix
1+0 records in
1+0 records out
1048576 bytes (1.0 MB) copied, 0.0209197 s, 50.1 MB/s

real    0m2.032s
user    0m2.015s
sys     0m0.025s

May someone can give me a hint or a better performing solution!

Edit: My fastest solution is about 10 times as fast as the initial solution:

#!/usr/bin/python
import array
import sys

rtrans = [0, 128, 64, 192, 32, 160, 96, 224, 16, 144, 80, 208, 48, 176, 112, 240, 8, 136, 72, 200, 40, 168, 104, 232, 24, 152, 88, 216, 56, 184, 120, 248, 4, 132, 68, 196, 36, 164, 100, 228, 20, 148, 84, 212, 52, 180, 116, 244, 12, 140, 76, 204, 44, 172, 108, 236, 28, 156, 92, 220, 60, 188, 124, 252, 2, 130, 66, 194, 34, 162, 98, 226, 18, 146, 82, 210, 50, 178, 114, 242, 10, 138, 74, 202, 42, 170, 106, 234, 26, 154, 90, 218, 58, 186, 122, 250, 6, 134, 70, 198, 38, 166, 102, 230, 22, 150, 86, 214, 54, 182, 118, 246, 14, 142, 78, 206, 46, 174, 110, 238, 30, 158, 94, 222, 62, 190, 126, 254, 1, 129, 65, 193, 33, 161, 97, 225, 17, 145, 81, 209, 49, 177, 113, 241, 9, 137, 73, 201, 41, 169, 105, 233, 25, 153, 89, 217, 57, 185, 121, 249, 5, 133, 69, 197, 37, 165, 101, 229, 21, 149, 85, 213, 53, 181, 117, 245, 13, 141, 77, 205, 45, 173, 109, 237, 29, 157, 93, 221, 61, 189, 125, 253, 3, 131, 67, 195, 35, 163, 99, 227, 19, 147, 83, 211, 51, 179, 115, 243, 11, 139, 75, 203, 43, 171, 107, 235, 27, 155, 91, 219, 59, 187, 123, 251, 7, 135, 71, 199, 39, 167, 103, 231, 23, 151, 87, 215, 55, 183, 119, 247, 15, 143, 79, 207, 47, 175, 111, 239, 31, 159, 95, 223, 63, 191, 127, 255]                                                                                      

sys.stdout.write(array.array('B', map(lambda x: rtrans[x], array.array('B', sys.stdin.read()[::-1]))).tostring())


time dd if=/dev/urandom count=1 bs=1M  | ./fastest.py > nix
1+0 records in
1+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.0148036 s, 70.8 MB/s

real    0m0.185s
user    0m0.171s
sys     0m0.027s

check this

Rohit-Pandey
– Rohit-Pandey

2018-10-21 17:53:52 +00:00
Commented Oct 21, 2018 at 17:53 — Rohit-Pandey
– Rohit-Pandey, Commented Oct 21, 2018 at 17:53

Vikrant Sharma · Accepted Answer · 2018-10-21 18:00:56Z

1

Using a single write()?

chars = [chr(int('{:08b}'.format(ord(i))[::-1], 2)) for i in reversed(data)]
sys.stdout.write(''.join(chars))

Here's what I'm getting on my machine.

Before:

1+0 records in 1+0 records out 1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.0961667 s, 10.9 MB/s real 0m1.233s user 0m1.144s sys 0m0.100s

After:

1+0 records in 1+0 records out 1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.0931753 s, 11.3 MB/s real 0m0.961s user 0m0.860s sys 0m0.104s

answered Oct 21, 2018 at 18:00

Vikrant Sharma

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