I am trying to solve this hackerrank problem: https://www.hackerrank.com/challenges/find-substring/problem.

As per the question, our task is to count the number of times a given query is found in the given string. The query should be inside a word, meaning if the query is gold, hgoldh matches, but goldh or hgold do not match. They further clarify that they mean alphabets, numbers and underscore (_) to be included as words, rest characters are not considered a part of word.

So, I came up with this pattern:

(?<=[a-zA-Z0-9_])({0})(?=[a-zA-Z0-9_])

Where {0} is replaced by the query.

Here is the complete code:

import re

## get input
n = int(input())
input_str: str = ""
for i in range(n):
    input_str += input()
q = int(input())
queries = []
for i in range(q):
    queries.append(input())

for crr_query in queries:
    regexp = r'(?<=[a-zA-Z0-9_])({0})(?=[a-zA-Z0-9_])'.format(crr_query)
    matches = re.findall(regexp, input_str)
    print(len(matches))

My code fails 9/10 tests. Here is one of the inputs:

40
satisfied)profit profit'container fashion.profit'egg profit-ms profit_unimportant leaf(profit profit.fall bear_profit offend_profit audience(profit'manager
interested(lack interested.normal slowly-interested interested'schedule untidy,interested sign(interested interested_tube boil(interestedthey interestedconfined pretty.interested,stressed
journalist)profit(cat crop(profit class)profit altogether(profit pound,profit-assure strange'profit kindly'profit-over profit)potentially credit,profit-homework profit.devote
goldclimbing extent_gold manage(gold.relaxing scream'gold insect_gold look'gold-town conventional-gold noticeablegoldpromptly intention.gold gold.make
organizationinterested'important interested-climb bankinterested picture.interested irritate'interested,variation encouragementinterested interested-beautiful noise-interested)luggage interested.variation cellphone-interested
media(profit staff-profit search-profit foreignprofit my'profit_find profit'ct disappointment'profit.climb blackprofit profit-have tin.profit
promptly(adult_pronunciation through)adult adult)repair hand)adult section(adult(difficult interval_adult.retired adult_task adult)further adult'sexual faith_adult
after)profit trick,profit profit)electronic profit'grab lake'profit_price avoid'profit'chop whistle,profit.confined profitoccasion combination,profit'direction curb_profit)straight
profit)spare profit.aspect floodprofit-care profitlocate profit-fundamental dog,profitgroup profitadequate petrol)profit-object profitreasonable profit'female
capture.gold actively.gold.separation gold.cold gold)particular gold)faithful frame,gold glue.gold gold.model sail-gold.nature lane(gold)sink
spirit.adult adult(basis adult-rush adult,get adult)make waist,adult.quiet throat(adult reality(adult adult)rob adult'closet
way-profit.go seriously)profit.desert bitter.profit atomprofit,interior cheque,profit(hatred publication,profit improve,profit variation_profit_good rubber(profitblue profit)quality
resource-profit profitwing profit'absence fever_profit profit-chief profit.goal entertainment'profit)neighbourhood gentleman,profit assume,profit_understanding hello-profit
adult_fever stupid-adult,expense adultcentury create,adult visionadult perfectlyadult instead,adult south_adult.ice map,adult adult-blood
coldlyinterested.nevertheless countyinterested)educated unlikely.interested_landscape interested-themselves interested_homework pension.interested annoyinterested(again mid_interested interested_weapon hammer_interested(swollen
themselves,profit weakness'profit insert_profit)record regulation_profit profit-beneath sharp)profit_wrapping obvious-profit.project remind'profit.tendency giveprofit_lie profit'confidently
avoid'profit.resort contract)profit float.profit complexprofit profit,save profit.staff profit_expensive mark'profit(brain profit,mg indirect.profit-apartment
profit-virtually rough,profit,excuse profit)pool profit-thickness hero_profit profit'lose profit(tea profit(re earth,profit)breathing restriction)profit
determined'profit,collapse poetry)profit profit.case profit,cap profit.burn profit-stock flour)profit_construction profit,alone profitinfection flight'profit
recover'interested,persuade suck)interested interested'film engaged(interested'traditionally pollution(interested'task interested)give working_interested interested-relaxing ininterested certainly.interested.paper
till,profit)wander aged,profit profit-patient profit-cost profit,head research(profit method_profit)mid annual_profit briefly(profit,spoon along)profit
offence,adult adult.article granddaughter.adult dentist)adult-mr thank-adult commercial(adult draft.adult'document licence-adult which.adult.well unload'adult.tire
gold'statue make.gold whilstgoldrefrigerator themselves_gold goldexamination furniture.gold cat'goldamazed wound)gold_department gold'tuesday potato(gold_wrap
serious_adult-wrap real-adult'warm exactly)adult adultengine chair-adult button-adult,take adult'afternoon adult.regulation impose-adult adultconsiderable
uncontrolled'adult,help division,adultthorough corner,adult_equipment amuse_adult except-adult_cloth language.adult attorney.adult boot_adult)permanent rely,adult southernadult
profit(achievement kilometre.profit each)profit profit'obtain class_profit-few south(profit,yours profitrace profit_contract profit(willingness profit(capture
nutprofit.deliberately profitwhich magic.profit sweater)profit profit)translation profit_wash profit)barrier profit-decorative c(profit proportion-profitpresence
increaseadult addition_adult)come separated(adult providedadult prepare_adult)shame lonely-adult complete.adult.after adult)forgive hire'adultmuch religion'adult'arms
suited)adult salary'adult adultsafety western-adult_technique zeroadult(humorous adult.drugstore adult_theme adult_stranger adulttoy technology,adult
amusing(adult fire.adult_suffer hard)adult upon)adult noadult'until spelling)adult-glasses adult-brave throw'adult yours.adult all-adult(wooden
interestedconference interested'necessarily interested'visitor publicity,interested roof)interestedlunch etc_interestedapply curl'interestedtiny considerable_interested containinterested interested_earth
depressing-adult rid-adult,agent pretend_adult_fancy adult-remain orange_adult take-adult onlyadult(be adult.sewing adult(decrease pick'adult)physical
interestedrid park,interested public-interested'woman fork,interested)thing would(interested)pan expected-interested interested.illegally interestedplastic enjoyment(interested interested_trace
ruin-interested'basic interestedbacteria interested(sheet interested)contrasting interested)presentation interested_prior nuclear,interested bite.interested-never interested-reception mysterious-interested
interested)insist our_interested pace(interested,fish interested.in interestedretirement interior'interested theme-interested interested(appointment interested-none pollution)interested
adult,possible adult.gentle adult(reduce willingness,adult hideadult adult.luggage fame.adult beach.adult adult_plate fly,adult
profita adequateprofit achieve)profit_style profit_expression central,profit sweep.profit indirectly(profit sound_profit.academic profitcontinue fold)profit_woman
interested_skilled interested'engineering interested_objective signalinterested'unhappiness fee)interested wholeinterested)effort interested)depress novel)interested solution)interested'enjoyable awkwardly(interested
adult.congratulations sing_adult adult)voice political.adult adult-knee adult(miss enough)adult adult,satisfying adult)cheque ordinary-adult)expensive
historical)adult_representative student(adult green_adult confirm_adult.deaf adult_proportion shiny_adult)counter unemployed,adult.foot friendly-adult adult)pig oppositeadult
4
gold
profit
adult
interested

and the expected output:

2
2
1
1

and my output:

3
3
4
4

I’ll be focusing on the first given query – gold only.

In my opinion, the regex pattern is correct. So, I go to regexr.com, enter the above input and my regex pattern (replacing {0} with gold in the pattern, which should also happen during the program’s execution), and to my surprise, I get the correct number of matches – 2!

I tried several variants of the same regex pattern many times, but have reached no conclusion. For eg, I tried (?<!b)({0})(?!b) as well – got the same results.

So, my question is:

Why is the number of matches using python 3, while using regexr.com it is 2? Does python interpret the regex pattern differently? Is there a problem in my python code?

Thank you for your time and efforts!