Python extracting specific line in text file

Question

I am writing a code that read a large text file line by line and find the line that starts with UNIQUE-ID (there are many of them in the file) and it comes right before a certain line (in this example, the one that starts with 'REACTION-LAYOUT -' and in which the 5th element in the string is OLEANDOMYCIN). The code is the following:

data2 = open('pathways.dat', 'r', errors = 'ignore')

pathways = data2.readlines()

PWY_ID = []
line_cont = []
L_PRMR = [] #Left primary
car = []

#i is the line number (first element of enumerate), 
#while line is the line content (2nd elem of enumerate)

for i,line in enumerate(pathways):
    if 'UNIQUE-ID' in line:
        line_cont = line
        PWY_ID_line = line_cont.rstrip()
        PWY_ID_line = PWY_ID_line.split(' ')
        PWY_ID.append(PWY_ID_line[2])
    elif 'REACTION-LAYOUT -' in line:
        L_PWY = line.rstrip()
        L_PWY = L_PWY.split(' ')
        L_PRMR.append(L_PWY[4])
    elif 'OLEANDOMYCIN' in line:
        car.append(PWY_ID)
print(car)

However, the output is instead all the lines that contain PWY_ID (output of the first if statement), like it was ignoring all the rest of the code. Can anybody help?

Edit

---

Below is a sample of my data (there are like 1000-ish similar "pages" in my textfile):

//
UNIQUE-ID - PWY-741
.
.
.
.
PREDECESSORS - (RXN-663 RXN-662)
REACTION-LAYOUT - (RXN-663 (:LEFT-PRIMARIES CPD-1003) (:DIRECTION :L2R) (:RIGHT-PRIMARIES CPD-1004))
REACTION-LAYOUT - (RXN-662 (:LEFT-PRIMARIES CPD-1002) (:DIRECTION :L2R) (:RIGHT-PRIMARIES CPD-1003))
REACTION-LAYOUT - (RXN-661 (:LEFT-PRIMARIES CPD-1001) (:DIRECTION :L2R) (:RIGHT-PRIMARIES CPD-1002))
REACTION-LIST - RXN-663
REACTION-LIST - RXN-662
REACTION-LIST - RXN-661
SPECIES - TAX-351746
SPECIES - TAX-644631
SPECIES - ORG-6335
SUPER-PATHWAYS - PWY-5266
TAXONOMIC-RANGE - TAX-1224
//

Answer 1

I think it would have been helpful if you'd posted some examples of data. But an approximation to what you're looking for is:

with open('pathways.dat','r', errors='ignore') as infile:
  i = infile.read().find(string_to_search)
  infile.seek(i+number_of_chars_to_read)

I hope this piece of code will help you focus your script on this line.

Answer 2

print(car) is printing out the list of all lines added by PWD_ID.append(PWY_ID_line[2]) in the first if, since you are appending the whole list of PWD_ID to car when you do car.append(PWY_ID) . so, if you want to print out the list of lines with OLEANDOMYCIN, you might want to just do car.append(line).