How to resolve TypeError when migrating code to Python3

Question

I moved my python scripts from 2.7 to 3 using 2to3 module, and now I am trying them out...Can some explain what I need to change here?

found_qr = None
while not found_qr:
    keep_alive(1,5)
    time.sleep(4)
    process = None
    stdout_list = None
    process = subprocess.Popen('grep -E -o ".Source QR CODE :.{0,65}" ' + latest_file + ' | tail -1', shell=True, stdout=subprocess.PIPE,)
    stdout_list = process.communicate()
    stdout_list = stdout_list[0]
    if stdout_list.find("Source QR CODE") == -1:
        found_qr = None
    else:
        found_qr = 'found!'

I am getting this error:

if stdout_list.find("Source QR CODE") == -1:
TypeError: argument should be integer or bytes-like object, not 'str'

any idea? thanks!

Update: Here is a similar issue I am seeing:

keep_alive(1,1)
process = subprocess.Popen('grep -E -o ".Source QR CODE :.{0,65}" ' + latest_file + ' | tail -1', shell=True, stdout=subprocess.PIPE,)
stdout_list = process.communicate()
qr_code = stdout_list[0].replace('Source QR CODE : ','')
qr_code = qr_code.replace(' ','')
qr_code = qr_code.replace('\n', '')
qr_code = str(qr_code)

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

ForceBru · Accepted Answer · 2020-02-03 17:19:15Z

1

In stdout_list = process.communicate() you get a list of bytes, so stdout_list[0] is a bytes object.

In stdout_list.find("Source QR CODE") you're trying to find a string in this bytes object, which won't work because bytes is different from str in Python 3.

Since this string is constant, you can convert it to a bytes object easily:

stdout_list.find(b"Source QR CODE")  # note the `b` before the string literal

Or encode this string appropriately:

stdout_list.find("Source QR CODE".encode('ascii'))  # here you can use whatever encoding you need

As the error message tells you, you can search for "bytes-like objects" and integers, because a bytes object is actually a list of integers from 0 to 255:

>>> b'thing'  # this is a bytes object
b'thing'
>>> list(_)
[116, 104, 105, 110, 103]  # actually a bunch of integers (bytes)
>>> b'thing'.find(116)  # find a single byte
0

answered Feb 3, 2020 at 17:19

ForceBru

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7 Comments

cjg123 Over a year ago

That seems to have worked...but can you help with this (similar issue): process = subprocess.Popen('grep -E -o ".Source QR CODE :.{0,65}" ' + latest_file + ' | tail -1', shell=True, stdout=subprocess.PIPE,) stdout_list = process.communicate() qr_code = stdout_list[0].replace('Source QR CODE : ','') qr_code = qr_code.replace(' ','') qr_code = qr_code.replace('\n', '') qr_code = str(qr_code)

ForceBru Over a year ago

@cjg123, you can run your code through 2to3 first. It should convert most of the code to Python 3 automatically

cjg123 Over a year ago

I did, but a lot of it was not changed...why would that be?

ForceBru Over a year ago

@cjg123, well, it's not perfect. For example, it doesn't seem to be able to infer that stdout_list is a bytes object. Anyway, for each error message of this kind, you should add a prefix b to each string literal in that line. For example: qr_code = stdout_list[0].replace('Source QR CODE : ','') -> qr_code = stdout_list[0].replace(b'Source QR CODE : ', b'')

ForceBru Over a year ago

@cjg123, actually, qr_code = str(qr_code) will result in "b'thing'", not just b'thing'. Why? Well, Python did what you asked it to do - it returned the string representation of that bytes object - the "b'thing'", while you expected just "thing", but that would be a different operation - decoding.

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