python enumerate looping through a file [duplicate]

Question

How does this enumerate works? I want a specific starting index but yet the loop goes too far(index out of range)

def endingIndexOfTable(file, index):
    
    r = re.compile('^V.*(.).*(.).*(.).*(-).*(-).*(.).*(.).*(:).*$')
    for i, line in enumerate(file, start= index):
        if list(filter(r.match, line)) or "Sales Tax" in line:
            return i

I want my program to start searching from line index and to return the line where I find the string I am looking for.

Answer 1

I don't think you can start at a specific line of a file. I think you have to skip all the preceding lines first:

def endingIndexOfTable(file, index):
    
    r = re.compile('^V.*(.).*(.).*(.).*(-).*(-).*(.).*(.).*(:).*$')
    for i, line in enumerate(file):
        if i >= index:
            if list(filter(r.match, line)) or "Sales Tax" in line:
                return i

Although, did you mean return line?

Then, the version with islice should be like this:

from itertools import islice

def endingIndexOfTable(file, index):
    
    r = re.compile('^V.*(.).*(.).*(.).*(-).*(-).*(.).*(.).*(:).*$')
    for i, line in islice(enumerate(file), index, None):
        if list(filter(r.match, line)) or "Sales Tax" in line:
            return i

(again assuming that both the regex and the return are correct)

Answer 2

EDIT

I screwed up in the same way as OP. This does not answer the question.

---

I don't want to deal with your regex, but here's one way to achieve the logic you need for searching from a specific line. It would load the entire file in memory though, and not actually read just the specific line.

poem.txt is just the file I used to test. Contents:

Author of the poem is: Me 
 poem is called: Test
AAFgz
S2zergtrxbhcn
Dzrgxt
Frhgc
Gzxcnhvjzx
xghrfcan a
jvzxhdyrfcv
kh

def read_by_line(file, index):
    for i, line in enumerate(file.readlines(), start=index):
        print(line)
        if "a" in line:  # if condition could have been your regex stuff
            return i

with open('poem.txt', 'r') as file_object:
    print(read_by_line(file_object, 5))