My script works well in Python 2 but not in python 3- TypeError

This is arising because while reading the logfile, you must have openedn the file in "rb" mode. This means in binary mode.

Now while doing comparison also it is asking to provide a binary substring for checking.

Now, you can solve this in 2 ways :

1. Either convert your search string into binary.

self.cut.start_line=b'test started'

2. Open the logfile for reading in simple mode, i.e., not binary mode [use "r" instead of "rb"].

line must be a str or start_line must be a bytes object

Two options:

Use b'test started'

self.cut.start_line=b'test started'

def extract_data(self):
    data=None
    for line in self.file_content:
        if data is None: 
            if self.start_line in line:   #search for 'test started'
                data=[]     
        elif self.end_line in line:    
            break   
        else:       
            data.append(line)
    return data

Use line.decode()

self.cut.start_line='test started'

def extract_data(self):
    data=None
    for line in self.file_content:
        line = line.decode()
        if data is None: 
            if self.start_line in line:   #search for 'test started'
                data=[]     
        elif self.end_line in line:    
            break   
        else:       
            data.append(line)
    return data

Use the encode() function to encode the string to bytes.

self.cut.start_line='test started'.encode()

If you want to get back the original string, use the decode() function. If self.cut.start_line is the encoded text, then

self.cut.start_line.decode()

will give back the original string.