TypeError a bytes-like object is required not str when writing to a file in Python3

Question

I have very recently switched to the Py 3.5 version but I noticed that the code mentioned below was working properly in Python 2.7:

with open(fname, 'rb') as f:
        lines = [x.strip() for x in f.readlines()] 

for line in lines: 
      tmp = line.strip().lower() 
      if 'some-pattern' in tmp: continue 
      # ... code

After switching to 3.5, I'm getting the following ERROR:-

TypeError: a bytes-like object is required, not 'str'

error on the last line (the pattern search code).

I have tried to use the .decode() function on either side of the statement along with the line mentioned below:

if tmp.find('some-pattern') != -1: continue

- to no avail.

I was able to resolve almost all 2:3 issues quickly, but this little statement is bugging me. Any solution for a way forward beyond this step?

Answer 1

After what I observed, you would have opened your file in the binary mode:-

with open(fname, 'rb') as f:

This would state that all the data which the file is reading has been returned as bytes objects, not str. You will not be able to use a string in a containment test:
 

if 'some-pattern' in tmp: continue

Now you will have to use a bytes object to test against tmp instead:
 

if b'some-pattern' in tmp: continue

You could also open the file as a text file instead by replacing the 'rb' mode with 'r'.