How to detect if last line of file contains text

Question

I am new to python and am trying to make a YT username to channel ID converter, It takes a txt input of channels/usernames and I want it to send the results from the API to the output.txt. But it reads from the whole output instead of just the newest/last line.

I tried using readlines(-1) but it seems to just not do anything at all.

from googleapiclient.discovery import build
import time

Channellist = open('input.txt','r').readline()
output = open('output.txt','r').read()

api_key = 'KEY'
youtube = build('youtube', 'v3', developerKey=api_key)
request = youtube.channels().list(
    part='snippet',
    id=(Channellist))
response = request.execute()


with open('output.txt', 'a', encoding="utf-8" ) as f:
    f.write(str(response) + '\n')


if output.__contains__("snippet") == True:
        print('Valid Channel ID/Username Found')
        time.sleep(1)
        print(response)
        with open('output.txt','r') as fp1:
         x = len(fp1.readlines())
         time.sleep(0.5)
         print('Total in Output:', x)
else:
    print('Invalid Channel ID/Username')
    with open('output.txt','r+') as fp:
        lines = fp.readlines()
        fp.seek(0)
        fp.truncate()
        fp.writelines(lines[:-1])

with open('input.txt', 'r') as fin:
    data = fin.read().splitlines(True)
with open('input.txt','w') as fout:
    fout.writelines(data[1:])


    exit()

with open('input.txt', 'r') as fin:
    data = fin.read().splitlines(True)
with open('input.txt','w') as fout:
    fout.writelines(data[1:])
exit()

I honestly just downloaded python 2 days ago and haven't done any tutorials. So I really don't know what's going wrong.

Can you explain in English what exactly each part of this code is supposed to be doing? It's pretty clear that there's some confusion about what specific statements/functions do, but it's not possible to write a corrected version without knowing what exactly you were trying to do. E.g. when you wrote `output.__contains__('snippet')`, is that something you're trying to do on each line of the file, or on the last line of the file, or on the file as a whole? And which file? — Samwise, Jul 05 '23 at 00:25
I tried to get it to only check if it contains 'snippet' on the last line of the output.txt file. Output is above and is just where the API response goes. I can barely understand my own code haha — dan, Jul 05 '23 at 00:46

score 0 · Answer 1 · answered Jul 05 '23 at 00:52

If I understand you, you just want to read the last line of a text file. here are two ways this could be done:

Splitting the file into lines, and then taking the last line:

with open('filename.txt') as f:
    lines = f.read().split("\n")
    last_line = lines[-1]  # NOTE: If your file ends in a newline, last_line will be empty
    # Do whatever you want with the last line:
    print(last_line)

Note that if the file ends in a newline last_line will be an empty string. If you need to handle files with newlines change the line:

lines = f.read().split("\n")

to:

lines = f.read().strip().split("\n")

Reading each line until the end:

As suggested here:

with open('filename.txt') as f:
    for line in f:
        pass
    last_line = line

How to detect if last line of file contains text

1 Answers1