Pycharm expected type 'optional[bytes]' got 'str' instead

Question

I am using rsplit to split up a path name,

rootPath = os.path.abspath(__file__)
rootPath = (rootPath.rsplit('/', 1)[0]).rsplit('/', 1)[0]

But Pycharm warns,

expected type optional [bytes], got str instead

In python doc, it stated using sep as the delimiter string.

So how to fix this?

Asked By: daiyue

||

Source

Answer 1

It seems like rootPath is being treated as a bytes object (a small bug maybe?) or the warning is for another part.

In general, what PyCharm and the error is essentially warning you about is that the parameter has to either be None or bytes. That’s what Optional means, Optional[type] is either None or type which in your case is bytes.

In a simple Python REPL the message is slightly different but the gist is the same:

b'hello/world'.rsplit('/') # error bytes-like object required

Instead you need to supply a byte separator:

b'hello/world'.rsplit(b'/')

or None in order to get it to work.

Either there’s a small bug in PyCharm and it’s reporting rsplit incorrectly here or the warning is for another part of your code.

Answered By: Dimitris Fasarakis Hilliard

Answer 2

I came here with the same problem and found a slightly different solution – thought of adding it for anyone that may land into the same issue in future.

rootPath = os.path.abspath(__file__)
rootPath = str(rootPath.rsplit('/', 1)[0]).rsplit('/', 1)[0]

Answered By: ObviousChild

Answer 3

I came across this earlier:

import subprocess

result = subprocess.run(
    "ls /etc/systemd/system",
    shell=True, capture_output=True, text=True
)

for line in result.stdout.split("n"):
    if "banana" in line:
        print(line.split(".")[0].strip().split("_"))

PyCharm began highlighting: "n", "banana", ".", "_":

It says it expects Optional[bytes] or Union[bytes,int], and yet this code runs perfectly well in python 3.10, 3.9, and 3.8.

I suspected it was my recent selection of Settings->Editor->Inspections->Code compatibility inspection so I disabled it and restarted that window to no avail.

I have added .decode() after .stdout to convert bytes. That quietens PyCharm, but is noise upon noise. In python 3.10 .stdout is not bytes but str and I’d get an error:

AttributeError: ‘str’ object has no attribute ‘decode’.

In the python docs I find the same method names in bytes that I do in str

Answered By: John

Pycharm expected type 'optional[bytes]' got 'str' instead

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