|
Description:
This module provides several functions that can
encode and decode a string. It also has a
function called partition for designing faster
algorithms. For sample usage of this module,
z_service.py provides example code.
Source: Text Source
'''Module for string manipulation.
This module provides several functions that
can encode, decode, and convert strings.'''
__version__ = 1.3
def string_code(string):
'Convert from string to code.'
return number_code(string_number(string))
def code_string(code):
'Convert from code to string.'
return number_string(code_number(code))
def string_number(string):
'Convert from string to number.'
number = 1L
for character in string:
number <<= 8
number += ord(character)
return number
def number_code(number):
'Convert from number to code.'
code = ''
while number:
code = chr(number % 255 + 1) + code
number /= 255
return code
def code_number(code):
'Convert from code to number.'
number = 0L
for character in code:
number *= 255
number += ord(character) - 1
return number
def number_string(number):
'Convert from number to string.'
string = ''
while number > 1:
string = chr(number & 0xFF) + string
number >>= 8
return string
def partition(string, size):
'Partitions a string into substrings.'
for index in range(0, len(string), size):
yield string[index:index+size]
if __name__ == '__main__':
import sys
print 'Content-Type: text/plain'
print
print file(sys.argv[0]).read()
Discussion:
This recipe used an algorithm that may be difficult
to replicate in some languages, but the approach is
rather unique in how information is encoded. The
general idea behind the procedure is to convert the
text into a number and then rewrite it in a different
base. Strings can be thought of as base 256 numbers
and can be stored as such using long numbers.
Converting those numbers into a lower base is as
simple as some modular arithmetic and divition. What
results is a string that can be very hard to figure
out for people trying to backward-engineer the encoding.
|
