DNA doesn't work with large database

Question

My program gives valid output with small databases, but with large I always get "No match". Do you have any idea what may be the cause ? Belowe is my code, It may seem a little messy so if you find it difficult to understand some of functions just ask and I'll try to explain it as best as I can.

import sys
import csv
import re
#check command line argument
if len(sys.argv)!=3:
   print ("Usage: python dna.py data.csv sequence.txt")

genomes_names = []
#open csv file with names and numbers of repetitions
with open(sys.argv[1], "r") as csvfile:
   dna_data = csv.reader(csvfile)
   personal_data = list(dna_data)
   #print(f"personal data {personal_data}")
   genomes_names = (personal_data[0][1:])
   #print(f"Genomes names {genomes_names}")

counter = 0
#open a file with sequences
file = open(sys.argv[2],"r")
sequence = file.read()

occurences = []
#read name of genomes and check the number of occurences
#function that counts repetitions I got from 
 https://stackoverflow.com/questions/51690245/consecutive- 
 substring-in-python

 for i in range(0,len(genomes_names)):
   start = 0
   substr_count = 0
   while True:
       string = sequence
       substring = genomes_names[i]
       #print(f"I check for: {genomes_names[i]}")
       loc = string.find(substring,start)
       if loc == -1:
          break
       substr_count += 1
       start = loc + 1
       #print(f"Checking for {genomes_names[i]}")
    #print(f"For {substring} number of repetitions is: {substr_count}")
    occurences.append(substr_count)
    substr_count = 0

 #print(f"Occurences of every pattern: {occurences}")

#how many rows are there
rows_number = len(personal_data)

repetitions = []

#print(f"occurences {occurences}")
match = 0
name = 0
no_match = False
 for i in range(1,len(personal_data)):
     #print(personal_data[i])
     for j in range(1,len(personal_data[i])):
         repetitions.append(personal_data[i][j])
     #print(repetitions)
     for k in range(len(repetitions)):
         if int(repetitions[k]) == int(occurences[k]):
             match +=1
             no_match = True
         else:
             match = match
             no_match = False
     repetitions = []
     if match == len(occurences) and no_match == True:
         print(personal_data[i][0])
         name+=1
     else:
         no_match = False
         match = 0

 if no_match == False and name == 0:
     print("No match")

Answer 1

That code on StackOverflow is meant to calculate something else, I guess. We don't need overlap, in our case, we have to keep track of the longest contiguous repetition sequence. For that, we need separate variables for current and longest streak, and update the longest if the current surpasses it. Also, we have to check whether the current match happens to be exactly len(substring) characters after the last one, a longer distance would indicate a restart.

My version for the next start would add len(substring) instead of 1, so I can later check whether loc != start, and reset the current length in that case (before I increment the count and maybe update the max count).