如何使用 python 按 position 计算字符串中相同字符的数量？

Question

For example:

String 1: AGGCCT
          || | |
String 2: AGCCAT

These two strings are identical at 4 positions, so the function I want would return 4.

Is there a clever (ie, fast) method for doing this, other than the obvious method of iterating through both strings at the same time?

Thanks! Uri

Answer 1

I don't think any "clever" trick beats the obvious approach, if it's well executed:

sum(c1 == c2 for c1, c2 in itertools.izip(s1, s2))

Or, if the use of booleans for arithmetic irks you,

sum(1 for c1, c2 in itertools.izip(s1, s2) if c1 == c2)

Answer 2

Though I prefer delnan's generator expression, this works as well:

>>> from itertools import imap
>>> from operator import eq
>>> sum(imap(eq, 'abcde', 'aacce'))
3

Answer 3

If you're looking for better performance, I suspect it will be hard to beat numpy for this:

import numpy as np
a1 = np.frombuffer(s1, dtype=np.byte)
a2 = np.frombuffer(s2, dtype=np.byte)
print (a1==a2).sum()

On my system, this runs about 10x faster than using itertools.