如何在python中比较这些字符串？

Question

I have the following string:

1679.2235398,-1555.40390834,-1140.07728186,-1999.85500108

and I'm using a steganography technique to store it in an image. Now when I retrieve it back out of the image, sometimes I got it back in a complete form and I have no issue with that. Where in other occasions, the retrieved data are not fully retrieved (due to a modification/alteration being occurred on the image), so the result something look like this:

1679.2235398,-1555.I8\xf3\x1cj~\x9bc\x13\xac\x9e8I>[a\xfdV#\x1c\xe1\xea\xa0\x8ah\x02\xed\xd1\x1c\x84\x96\xe2\xfbk*8'l

Notice that, only "1679.2235398,-1555." are correctly retrieved, while the rest is where the modification has been occurred. Now, how do I compute (in percentage) how much I successfully retrieved? Since the length is not the same, I can't do a character by character comparison , it seems that I need to slice or convert the modified data into some other form to match the length of the original data.

Any tips?

Answer 1

A lot of this is going to depend on the context of your problem, but you have a number of options here.

If your results always look like that, you could just find the longest common subsequence , then divide by the length of the original string for a percentage.

Levenshtein distance is a common way of comparing strings, as the number of characters required to change to turn one string into another. This question has several answers discussing how to turn that into a percentage.

If you don't expect the strings to always come out in the same order, this answer suggests some algorithms used for DNA work.

Answer 2

Well it really depends.. My solution would be something like this:

I would start with all the longest string possible and check if they are in the new string if original_string in new_string: 'something happens here'. that would be inside a loop that wld decrease the size of the original string and get all combinations possible. so the next one wld be N-1 long and have 2 possible combinations (cutting off the first number or the last number), and so on, until u get to a specific threshold, or to 1 long strings.
the loop can store the longest string you find in a log inside the if conditional, and afterward you can just check the results. hope that helps.