python 3, differences between two strings

问题

I'd like to record the location of differences from both strings in a list (to remove them) ... preferably recording the highest separation point for each section, as these areas will have dynamic content.

Compare these

total chars 178. Two unique sections

t1 = 'WhereTisthetotalnumberofght5y5wsjhhhhjhkmhm Thethreemethodsthatreturntheratioofmatchingtototalcharacterscangivedifferentresultsduetodifferinglevelsofapxxxxxxxproximation,although'

and

total chars 211. Two unique sections

t2 = 'WhereTisthetotalnumberofdofodfgjnjndfgu><rgregw><sssssuguyguiygis>gggs<GS,Gs Thethreemethodsthatreturntheratioofmatchingtototalcharacterscangivedifferentrexxxxxxxsultsduetodifferinglevelsofapproximation,although'

I know difflib can do this but the output is bad.

I'd like to store (in a list) the char positions, perferably the larger seperation values.

pattern location

t1 = 'WhereTisthetotalnumberof  24  ght5y5wsjhhhhjhkmhm  43  Thethreemethodsthatreturntheratioofmatchingtototalcharacterscangivedifferentresultsduetodifferinglevelsofap  151  xxxxxxx  158  proximation,although'
t2 = 'WhereTisthetotalnumberof  24  dofodfgjnjndfgu><rgregw><sssssuguyguiygis>gggs<GS,Gs  76  Thethreemethodsthatreturntheratioofmatchingtototalcharacterscangivedifferentre  155  xxxxxxx  162  sultsduetodifferinglevelsofapproximation,although'

output:

output list = [24, 76, 151, 162]

Update

Response post @Olivier

position of all Y's seperated by ***

t1
WhereTisthetotalnumberofght5***y***5wsjhhhhjhkmhm Thethreemethodsthatreturntheratioofmatchingtototalcharacterscangivedifferentresultsduetodifferinglevelsofapxxxxxxxproximation,although

t2 WhereTisthetotalnumberofdofodfgjnjndfgu><rgregw><sssssugu***y***gui***y***gis>gggs<GS,Gs Thethreemethodsthatreturntheratioofmatchingtototalcharacterscangivedifferentrexxxxxxxsultsduetodifferinglevelsofapproximation,although

output after matcher.get_matching_blocks() and string = ''.join([t1[a:a+n] for a, _, n in blocks])

WhereTisthetotalnumberof***y*** Thethreemethodsthatreturntheratioofmatchingtototalcharacterscangivedifferentresultsduetodifferinglevelsofapproximation,although

回答1:

Using difflib is probably your best bet as you are unlikely to come up with a more efficient solution than the algorithms it provides. What you want is to use SequenceMatcher.get_matching_blocks. Here is what it will output according to the doc.

Return list of triples describing matching subsequences. Each triple is of the form (i, j, n), and means that a[i:i+n] == b[j:j+n]. The triples are monotonically increasing in i and j.

Here is a way you could use this to reconstruct a string from which you removed the delta.

from difflib import SequenceMatcher

x = "abc_def"
y = "abc--ef"

matcher = SequenceMatcher(None, x, y)
blocks = matcher.get_matching_blocks()

# blocks: [Match(a=0, b=0, size=4), Match(a=5, b=5, size=2), Match(a=7, b=7, size=0)]

string = ''.join([x[a:a+n] for a, _, n in blocks])

# string: "abcef"

Edit: It was also pointed out that in a case where you had two strings like such.

t1 = 'WordWordaayaaWordWord'
t2 = 'WordWordbbbybWordWord'

Then the above code would return 'WordWordyWordWord. This is because get_matching_blocks will catch that 'y' that is present in both strings between the expected blocks. A solution around this is to filter the returned blocks by length.

string = ''.join([x[a:a+n] for a, _, n in blocks if n > 1])

If you want more complex analysis of the returned blocks you could also do the following.

def block_filter(substring):
    """Outputs True if the substring is to be merged, False otherwise"""
    ...


string = ''.join([x[a:a+n] for a, _, n in blocks if block_filter(x[a:a+n])])

来源：https://stackoverflow.com/questions/48737881/python-3-differences-between-two-strings

标签

string

python-3.x

difflib