Python:Detect if the current line in file read is the last one

Question

I am reading a file in Python line by line and I need to know which line is the last one while reading,something like this:

 f = open("myfile.txt")
 for line in f:
    if line is lastline:
       #do smth

From the examples I found it involves seeks and complete file readouts to count lines,etc.Can I just detect that the current line is the last one? I tried to go and check for "\n" existence ,but in many cases the last lines is not followed by backslash N.

Sorry if my question is redundant as I didn't find the answer on SO

Answer 1

import os
path = 'myfile.txt'
size = os.path.getsize(path)
with open(path) as f:
    for line in f:
        size -= len(line)
        if not size:
            print('this is the last line')
            print(line)

Here is an alternative solution, in case it's a really large file, that takes a long time to traverse. The file is read in reverse from end to beginning using seek. It assumes the file is not binary and not compressed and has at least one line break and the very last character is a line break.

import os
path = 'myfile.txt'
size = os.path.getsize(path)
with open(path) as f:
    for i in range(1, size):
        f.seek(size - 1 - i)
        if f.read(1) == '\n':
            print('This is the last line.:')
            last_line = f.read()
            print(last_line)
            break