Unpacking SequenceMatcher loop results

Question

What is the best way to unpack SequenceMatcher loop results in Python so that values can be easily accessed and processed?

from difflib import *

orig = "1234567890"

commented = "123435456353453578901343154"

diff = SequenceMatcher(None, orig, commented)

match_id = []
for block in diff.get_matching_blocks():
    match_id.append(block)

print(match_id)

String integers represent Chinese Characters.

The current iteration code stores match results in a list like this:

match_id
[Match(a=0, b=0, size=4), Match(a=4, b=7, size=2), Match(a=6, b=16, size=4), Match(a=10, b=27, size=0)]

I'd eventually like to mark out the comments with "{{" and "}}" like so:

"1234{{354}}56{{3534535}}7890{{1343154}}"

Which means, I am interested in unpacking the above SequenceMatcher results and do some calculations on specific b and size values to yield this sequence:

rslt = [[0+4,7],[7+2,16],[16+4,27]]

which is a repetition of [b[i]+size[i],b[i+1]].

Answer 1

1. Unpacking SequenceMatcher results to yield a sequence

You can unzip match_id and then use a list comprehension with your expression.

a, b, size = zip(*match_id)
# a    = (0, 4,  6, 10)
# b    = (0, 7, 16, 27)
# size = (4, 2,  4,  0)

rslt = [[b[i] + size[i], b[i+1]] for i in range(len(match_id)-1)]
# rslt = [[4, 7], [9, 16], [20, 27]]

Reference for zip, a Python built-in function: https://docs.python.org/3/library/functions.html#zip

2. Marking out the comments with "{{" and "}}"

You can loop through rslt and then nicely append the match-so-far and mark out the comments.

rslt_str = ""
prev_end = 0

for start, end in rslt:
    rslt_str += commented[prev_end:start]
    if start != end:
        rslt_str += "{{%s}}" % commented[start:end]
    prev_end = end
# rslt_str = "1234{{354}}56{{3534535}}7890{{1343154}}"

Answer 2

I would do it like this:

from difflib import *

orig = "1234567890"
commented = "123435456353453578901343154"

diff = SequenceMatcher(None, orig, commented)

match_id = []
rslt_str = ""
for block in diff.get_matching_blocks():
    match_id.append(block)

temp = 0
for i, m in enumerate(match_id[:-1]):
    rslt_str += commented[temp:m.b + m.size] + "{{"
    rslt_str += commented[m.b + m.size: match_id[i+1].b] + "}}"
    temp = match_id[i+1].b

so that rslt_str == "1234{{354}}56{{3534535}}7890{{1343154}}"

Answer 3

You can try this:

from difflib import *

orig = "1234567890"
commented = "123435456353453578901343154"
diff = SequenceMatcher(None, orig, commented)

a, b, size = zip(*diff.get_matching_blocks())

start = {x + y : '{{' for x, y in zip(b[:-1],size)}
end = dict.fromkeys(b[1:], '}}')
rslt = {**start, **end}

final_str = ''.join(rslt.get(ix,'') + n for ix, n in enumerate(commented)) + '}}'

print(final_str)

Output:

'1234{{354}}56{{3534535}}7890{{1343154}}'

Explanation:

As SequenceMatcher().matching_blocks() is iterable, so you can directly unpack it to your variables.

1. Then create a dictionary with starting indices as keys and {{ as value.
2. Similarly, create a dictionary with ending indices as keys and }} as value.
3. Unpack both the dictionaries in rslt.

Then form a list by passing the characters of commented as default value to dict.get and for indices in the rslt dict, prepend character with corresponding curly braces. Finally join into string.