Working of methods set_seq1 and set_seq2 , difflib python

Question

I have checked the docs of difflib and i'm confused on how difflib.SequenceMatcher.ratio() actually works. Consider this :

s = difflib.SequenceMatcher(None, "hey here" , "hey there").ratio()
print s

gives s = 0.9411764705882353
I wanted to know how exactly it is computed . The 2 strings are compared by actually looking at the deviation of one string w.r.t other.for 2 strings a and b The docs say :

differences are computed as "what do we need to do to 'a' to change it into 'b'?"

And there is something like :

for x in b, b2j[x] is a list of the indices (into b) at which x appears; junk elements do not appear

Please explain w.r.t the above example of s .

Seems like you should use `'` instead of `"`. Look: `difflib.SequenceMatcher(None, 'hey there', 'hey there').ratio()` is exacly 1.0 — Dmitry Loparev, May 15 '14 at 15:34
its "hey here" and "hey there" , the quotes don't make a difference. you have typed the wrong words.. — Hypothetical Ninja, May 15 '14 at 15:39

score 1 · Accepted Answer · answered May 16 '14 at 14:21

From the docs:

Where T is the total number of elements in both sequences, and M is the number of matches, this is 2.0*M / T.

In this case, T is 17 because the first string has 8 characters and the second string has 9. M is 8 because eight characters from the first string match with characters from the second. 2 * 8 / 17 equals 0.9411764705882353.

Working of methods set_seq1 and set_seq2 , difflib python

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