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

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

You opened the file in binary mode:

with open(fname, rb) as f:

This means that all data read from the file is returned as bytes objects, not str. You cannot then use a string in a containment test:

if some-pattern in tmp: continue

Youd have to use a bytes object to test against tmp instead:

if bsome-pattern in tmp: continue

or open the file as a textfile instead by replacing the rb mode with r.

You can encode your string by using .encode()

Example:

Hello World.encode()

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

Like it has been already mentioned, you are reading the file in binary mode and then creating a list of bytes. In your following for loop you are comparing string to bytes and that is where the code is failing.

Decoding the bytes while adding to the list should work. The changed code should look as follows:

with open(fname, rb) as f:
    lines = [x.decode(utf8).strip() for x in f.readlines()]

The bytes type was introduced in Python 3 and that is why your code worked in Python 2. In Python 2 there was no data type for bytes:

>>> s=bytes(hello)
>>> type(s)
<type str>