如何在python中将字符串转换为唯一的十进制数字？

Question

I need to convert a string, say for instance "Hello world" into a unique decimal number. By unique I mean that the number should be different even if a tiny bit of the string is changed. Furthermore, this process must be reversible. This is the process I need:

a = "Hello world"

b = someFunction(a)
print(b) --> 4324234

c = inverseOfSomeFunction(b)
print(c) --> "Hello world"

I looked through python documentation however I did not find an answer..

Answer 1

a="Hello WORLD"

def toBigInt(s):
    ret=0
    for i,j in enumerate(s):
        ret+= ord(j)<<(i*8)
    return ret

def fromBigInt(i):
    s=""
    while i>0:
        s+=chr(i&0xff)
        i=i>>8
    return s

i = toBigInt(a)
print i
print fromBigInt(i)

This works the following: ord() takes the integer representation for one character. Thats between 0 and 255.

The <<(i*8) shifts the next letter by 8 bits. Its the same as *i*265 just more to the point.

The decoding Function always takes the lowest 8 bits (i%0xff) and decodes them. Then it shifts the remaining number 8 bits down.