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

Question

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

Question

I've very recently migrated to Py 3.5. This code 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 upgrading to 3.5, I'm getting the:

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

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

I've tried using the .decode() function on either side of the statement, also tried:

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.

masroore

2019/08/21

Read less…

You can encode your string by using .encode()

Example:

'Hello World'.encode()

theofpa

2017/12/29

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'>

Suresh

2016/05/17

You have to change from wb to w:

def __init__(self):
    self.myCsv = csv.writer(open('Item.csv', 'wb')) 
    self.myCsv.writerow(['title', 'link'])

to

def __init__(self):
    self.myCsv = csv.writer(open('Item.csv', 'w'))
    self.myCsv.writerow(['title', 'link'])

After changing this, the error disappears, but you can't write to the file (in my case). So after all, I don't have an answer?

Source: How to remove ^M

Changing to 'rb' brings me the other error: io.UnsupportedOperation: write

meck373

2017/05/23

for this small example: import socket

mysock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
mysock.connect(('www.py4inf.com', 80))
mysock.send(**b**'GET http://www.py4inf.com/code/romeo.txt HTTP/1.0\n\n')

while True:
    data = mysock.recv(512)
    if ( len(data) < 1 ) :
        break
    print (data);

mysock.close()

adding the "b" before 'GET http://www.py4inf.com/code/romeo.txt HTTP/1.0\n\n' solved my problem

starter

2016/03/22

Use encode() function along with hardcoded String value given in a single quote.

Ex:

file.write(answers[i] + '\n'.encode())

OR

line.split(' +++$+++ '.encode())

Shiv Buyya

2019/04/20

Martijn Pieters · Accepted Answer · 10/10/2015 1:30:57 PM

Accepted Answer

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

You'd have to use a bytes object to test against tmp instead:

if b'some-pattern' in tmp: continue

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

Martijn Pieters

2015/10/10