Python比较两个字符串

Question

Is there a function to compare how many characters two strings (of the same length) differ by? I mean only substitutions. For example, AAA would differ from AAT by 1 character.

Answer 1

This will work:

>>> str1 = "AAA"
>>> str2 = "AAT"
>>> sum(1 for x,y in enumerate(str1) if str2[x] != y)
1
>>> str1 = "AAABBBCCC"
>>> str2 = "ABCABCABC"
>>> sum(1 for x,y in enumerate(str1) if str2[x] != y)
6
>>>

The above solution uses sum , enumerate , and a generator expression .

---

Because True can evaluate to 1 , you could even do:

>>> str1 = "AAA"
>>> str2 = "AAT"
>>> sum(str2[x] != y for x,y in enumerate(str1))
1
>>>

But I personally prefer the first solution because it is clearer.

Answer 2

This is a nice use case for the zip function!

def count_substitutions(s1, s2):
    return sum(x != y for (x, y) in zip(s1, s2))

Usage:

>>> count_substitutions('AAA', 'AAT')
1

From the docs:

zip(...)
    zip(seq1 [, seq2 [...]]) -> [(seq1[0], seq2[0] ...), (...)]

    Return a list of tuples, where each tuple contains the i-th element
    from each of the argument sequences.  The returned list is truncated
    in length to the length of the shortest argument sequence.

Answer 3

Building on what poke said I would suggest the jellyfish package. It has several distance measures like what you are asking for. Example from the documentation:

IN [1]: jellyfish.damerau_levenshtein_distance('jellyfish', 'jellyfihs')
OUT[1]: 1

or using your example:

IN [2]: jellyfish.damerau_levenshtein_distance('AAA','AAT')
OUT[2]: 1

This will work for many different string lengths and should be able to handle most of what you throw at it.

Answer 4

Similar to simon's answer, but you don't have to zip things in order to just call a function on the resulting tuples because that's what map does anyway (and itertools.imap in Python 2). And there's a handy function for != in operator . Hence:

sum(map(operator.ne, s1, s2))