start removal of six and improve type annotation (#607)

* fix unfinished Python2 -> 3 translation
* remove some six usage
* annotate
* fix regression in Six removal
* mypy: self.enf is always defined
* fix return type of cups.py
* Usb idVendor/idProduct are integers
* self.default_args is always defined
* tweak usb_args, PEP589 is better
* lp.py: reassure mypy
* correctly cast call to CashDrawerError()
* update CUPS test
* add missing close() method in metaclass
* document a bug in typeshed
* query_status() returns bytes as seen in constants.py
* remove more SIX usage
* test examples too
* remove type comment where type is annotated
* adapt behavior of cups printer to match other implementations

---------

Co-authored-by: Patrick Kanzler <dev@pkanzler.de>
Co-authored-by: Patrick Kanzler <4189642+patkan@users.noreply.github.com>

test/test_cli.py

@@ -7,7 +7,6 @@ import os
 import shutil
 import tempfile
 
-import pytest
 from scripttest import TestFileEnvironment as TFE
 
 import escpos
@@ -31,22 +30,19 @@ class TestCLI:
     """Contains setups, teardowns, and tests for CLI"""
 
     @classmethod
-    def setup_class(cls):
+    def setup_class(cls) -> None:
         """Create a config file to read from"""
         with open(CONFIGFILE, "w") as config:
             config.write(CONFIG_YAML)
 
     @classmethod
-    def teardown_class(cls):
+    def teardown_class(cls) -> None:
         """Remove config file"""
         os.remove(CONFIGFILE)
         shutil.rmtree(TEST_DIR)
 
-    def setup_method(self):
+    def setup_method(self) -> None:
         """Create a file to print to and set up env"""
-        self.env = None
-        self.default_args = None
-
         self.env = TFE(
             base_path=TEST_DIR,
             cwd=os.getcwd(),
@@ -64,24 +60,24 @@ class TestCLI:
         finally:
             fhandle.close()
 
-    def teardown_method(self):
+    def teardown_method(self) -> None:
         """Destroy printer file and env"""
         os.remove(DEVFILE)
         self.env.clear()
 
-    def test_cli_help(self):
+    def test_cli_help(self) -> None:
         """Test getting help from cli"""
         result = self.env.run("python-escpos", "-h")
         assert not result.stderr
         assert "usage" in result.stdout
 
-    def test_cli_version(self):
+    def test_cli_version(self) -> None:
         """Test the version string"""
         result = self.env.run("python-escpos", "version")
         assert not result.stderr
         assert escpos.__version__ == result.stdout.strip()
 
-    def test_cli_version_extended(self):
+    def test_cli_version_extended(self) -> None:
         """Test the extended version information"""
         result = self.env.run("python-escpos", "version_extended")
         assert not result.stderr
@@ -89,7 +85,7 @@ class TestCLI:
         # test that additional information on e.g. Serial is printed
         assert "Serial" in result.stdout
 
-    def test_cli_text(self):
+    def test_cli_text(self) -> None:
         """Make sure text returns what we sent it"""
         test_text = "this is some text"
         result = self.env.run(
@@ -108,7 +104,7 @@ class TestCLI:
             result.files_updated[DEVFILE_NAME].bytes == "\x1bt\x00" + test_text + "\n"
         )
 
-    def test_cli_text_invalid_args(self):
+    def test_cli_text_invalid_args(self) -> None:
         """Test a failure to send valid arguments"""
         result = self.env.run(
             *(self.default_args + ("text", "--invalid-param", "some data")),

test/test_function_buzzer.py

@@ -1,14 +1,13 @@
 import pytest
-import six
 
 from escpos import printer
 from escpos.constants import BUZZER
 
 
-def test_buzzer_function_with_default_params():
+def test_buzzer_function_with_default_params() -> None:
     instance = printer.Dummy()
     instance.buzzer()
-    expected = BUZZER + six.int2byte(2) + six.int2byte(4)
+    expected = BUZZER + bytes((2, 4))
     assert instance.output == expected
 
 
@@ -26,10 +25,10 @@ def test_buzzer_function_with_default_params():
         [9, 9],
     ],
 )
-def test_buzzer_function(times, duration):
+def test_buzzer_function(times: int, duration: int) -> None:
     instance = printer.Dummy()
     instance.buzzer(times, duration)
-    expected = BUZZER + six.int2byte(times) + six.int2byte(duration)
+    expected = BUZZER + bytes((times, duration))
     assert instance.output == expected
 
 
@@ -46,7 +45,9 @@ def test_buzzer_function(times, duration):
         [3, 11, "duration must be between 1 and 9"],
     ],
 )
-def test_buzzer_fuction_with_outrange_values(times, duration, expected_message):
+def test_buzzer_fuction_with_outrange_values(
+    times: int, duration: int, expected_message: str
+) -> None:
     instance = printer.Dummy()
     with pytest.raises(ValueError) as e:
         instance.buzzer(times, duration)

test/test_function_cut.py

@@ -1,5 +1,3 @@
-import six
-
 import escpos.printer as printer
 from escpos.constants import GS
 
@@ -8,5 +6,5 @@ def test_cut_without_feed():
     """Test cut without feeding paper"""
     instance = printer.Dummy()
     instance.cut(feed=False)
-    expected = GS + b"V" + six.int2byte(66) + b"\x00"
+    expected = GS + b"V" + bytes((66,)) + b"\x00"
     assert instance.output == expected

test/test_function_image.py

@@ -16,7 +16,7 @@ from escpos.exceptions import ImageWidthError
 
 
 # Raster format print
-def test_bit_image_black():
+def test_bit_image_black() -> None:
     """
     Test printing solid black bit image (raster)
     """
@@ -30,7 +30,7 @@ def test_bit_image_black():
     assert instance.output == b"\x1dv0\x00\x01\x00\x01\x00\x80"
 
 
-def test_bit_image_white():
+def test_bit_image_white() -> None:
     """
     Test printing solid white bit image (raster)
     """
@@ -39,7 +39,7 @@ def test_bit_image_white():
     assert instance.output == b"\x1dv0\x00\x01\x00\x01\x00\x00"
 
 
-def test_bit_image_both():
+def test_bit_image_both() -> None:
     """
     Test printing black/white bit image (raster)
     """
@@ -58,7 +58,7 @@ def test_bit_image_transparent():
 
 
 # Column format print
-def test_bit_image_colfmt_black():
+def test_bit_image_colfmt_black() -> None:
     """
     Test printing solid black bit image (column format)
     """
@@ -67,7 +67,7 @@ def test_bit_image_colfmt_black():
     assert instance.output == b"\x1b3\x10\x1b*!\x01\x00\x80\x00\x00\x0a\x1b2"
 
 
-def test_bit_image_colfmt_white():
+def test_bit_image_colfmt_white() -> None:
     """
     Test printing solid white bit image (column format)
     """
@@ -76,7 +76,7 @@ def test_bit_image_colfmt_white():
     assert instance.output == b"\x1b3\x10\x1b*!\x01\x00\x00\x00\x00\x0a\x1b2"
 
 
-def test_bit_image_colfmt_both():
+def test_bit_image_colfmt_both() -> None:
     """
     Test printing black/white bit image (column format)
     """
@@ -87,7 +87,7 @@ def test_bit_image_colfmt_both():
     )
 
 
-def test_bit_image_colfmt_transparent():
+def test_bit_image_colfmt_transparent() -> None:
     """
     Test printing black/transparent bit image (column format)
     """
@@ -99,7 +99,7 @@ def test_bit_image_colfmt_transparent():
 
 
 # Graphics print
-def test_graphics_black():
+def test_graphics_black() -> None:
     """
     Test printing solid black graphics
     """
@@ -111,7 +111,7 @@ def test_graphics_black():
     )
 
 
-def test_graphics_white():
+def test_graphics_white() -> None:
     """
     Test printing solid white graphics
     """
@@ -123,7 +123,7 @@ def test_graphics_white():
     )
 
 
-def test_graphics_both():
+def test_graphics_both() -> None:
     """
     Test printing black/white graphics
     """
@@ -135,7 +135,7 @@ def test_graphics_both():
     )
 
 
-def test_graphics_transparent():
+def test_graphics_transparent() -> None:
     """
     Test printing black/transparent graphics
     """
@@ -147,7 +147,7 @@ def test_graphics_transparent():
     )
 
 
-def test_large_graphics():
+def test_large_graphics() -> None:
     """
     Test whether 'large' graphics that induce a fragmentation are handled correctly.
     """
@@ -162,13 +162,13 @@ def test_large_graphics():
 
 
 @pytest.fixture
-def dummy_with_width():
+def dummy_with_width() -> printer.Dummy:
     instance = printer.Dummy()
     instance.profile.profile_data = {"media": {"width": {"pixels": 384}}}
     return instance
 
 
-def test_width_too_large(dummy_with_width):
+def test_width_too_large(dummy_with_width: printer.Dummy) -> None:
     """
     Test printing an image that is too large in width.
     """
@@ -180,7 +180,7 @@ def test_width_too_large(dummy_with_width):
     instance.image(Image.new("RGB", (384, 200)))
 
 
-def test_center_image(dummy_with_width):
+def test_center_image(dummy_with_width: printer.Dummy) -> None:
     instance = dummy_with_width
 
     with pytest.raises(ImageWidthError):

test/test_function_linedisplay.py

@@ -11,21 +11,21 @@
 import escpos.printer as printer
 
 
-def test_function_linedisplay_select_on():
+def test_function_linedisplay_select_on() -> None:
     """test the linedisplay_select function (activate)"""
     instance = printer.Dummy()
     instance.linedisplay_select(select_display=True)
     assert instance.output == b"\x1B\x3D\x02"
 
 
-def test_function_linedisplay_select_off():
+def test_function_linedisplay_select_off() -> None:
     """test the linedisplay_select function (deactivate)"""
     instance = printer.Dummy()
     instance.linedisplay_select(select_display=False)
     assert instance.output == b"\x1B\x3D\x01"
 
 
-def test_function_linedisplay_clear():
+def test_function_linedisplay_clear() -> None:
     """test the linedisplay_clear function"""
     instance = printer.Dummy()
     instance.linedisplay_clear()

test/test_function_set.py

@@ -1,3 +1,5 @@
+from typing import Optional
+
 import pytest
 import six
 
@@ -6,7 +8,7 @@ from escpos.constants import SET_FONT, TXT_NORMAL, TXT_SIZE, TXT_STYLE
 from escpos.exceptions import SetVariableError
 
 
-def test_default_values_with_default():
+def test_default_values_with_default() -> None:
     """Default test, please copy and paste this block to test set method calls"""
     instance = printer.Dummy()
     instance.set_with_default()
@@ -26,7 +28,7 @@ def test_default_values_with_default():
     assert instance.output == b"".join(expected_sequence)
 
 
-def test_default_values():
+def test_default_values() -> None:
     """Default test"""
     instance = printer.Dummy()
     instance.set()
@@ -37,7 +39,7 @@ def test_default_values():
 # Size tests
 
 
-def test_set_size_2h():
+def test_set_size_2h() -> None:
     instance = printer.Dummy()
     instance.set_with_default(double_height=True)
 
@@ -56,7 +58,7 @@ def test_set_size_2h():
     assert instance.output == b"".join(expected_sequence)
 
 
-def test_set_size_2h_no_default():
+def test_set_size_2h_no_default() -> None:
     instance = printer.Dummy()
     instance.set(double_height=True)
 
@@ -68,7 +70,7 @@ def test_set_size_2h_no_default():
     assert instance.output == b"".join(expected_sequence)
 
 
-def test_set_size_2w():
+def test_set_size_2w() -> None:
     instance = printer.Dummy()
     instance.set_with_default(double_width=True)
 
@@ -87,7 +89,7 @@ def test_set_size_2w():
     assert instance.output == b"".join(expected_sequence)
 
 
-def test_set_size_2w_no_default():
+def test_set_size_2w_no_default() -> None:
     instance = printer.Dummy()
     instance.set(double_width=True)
 
@@ -99,7 +101,7 @@ def test_set_size_2w_no_default():
     assert instance.output == b"".join(expected_sequence)
 
 
-def test_set_size_2x():
+def test_set_size_2x() -> None:
     instance = printer.Dummy()
     instance.set_with_default(double_height=True, double_width=True)
 
@@ -118,7 +120,7 @@ def test_set_size_2x():
     assert instance.output == b"".join(expected_sequence)
 
 
-def test_set_size_2x_no_default():
+def test_set_size_2x_no_default() -> None:
     instance = printer.Dummy()
     instance.set(double_width=True, double_height=True)
 
@@ -130,7 +132,7 @@ def test_set_size_2x_no_default():
     assert instance.output == b"".join(expected_sequence)
 
 
-def test_set_size_custom():
+def test_set_size_custom() -> None:
     instance = printer.Dummy()
     instance.set_with_default(custom_size=True, width=8, height=7)
 
@@ -151,7 +153,7 @@ def test_set_size_custom():
 
 @pytest.mark.parametrize("width", [1, 8])
 @pytest.mark.parametrize("height", [1, 8])
-def test_set_size_custom_no_default(width, height):
+def test_set_size_custom_no_default(width: int, height: int) -> None:
     instance = printer.Dummy()
     instance.set(custom_size=True, width=width, height=height)
 
@@ -165,7 +167,9 @@ def test_set_size_custom_no_default(width, height):
 
 @pytest.mark.parametrize("width", [None, 0, 9, 10, 4444])
 @pytest.mark.parametrize("height", [None, 0, 9, 10, 4444])
-def test_set_size_custom_invalid_input(width, height):
+def test_set_size_custom_invalid_input(
+    width: Optional[int], height: Optional[int]
+) -> None:
     instance = printer.Dummy()
     with pytest.raises(SetVariableError):
         instance.set(custom_size=True, width=width, height=height)
@@ -174,7 +178,7 @@ def test_set_size_custom_invalid_input(width, height):
 # Flip
 
 
-def test_set_flip():
+def test_set_flip() -> None:
     instance = printer.Dummy()
     instance.set_with_default(flip=True)
 
@@ -193,7 +197,7 @@ def test_set_flip():
     assert instance.output == b"".join(expected_sequence)
 
 
-def test_set_flip_no_default():
+def test_set_flip_no_default() -> None:
     instance = printer.Dummy()
     instance.set(flip=True)
 
@@ -205,7 +209,7 @@ def test_set_flip_no_default():
 # Smooth
 
 
-def test_smooth():
+def test_smooth() -> None:
     instance = printer.Dummy()
     instance.set_with_default(smooth=True)
 
@@ -227,7 +231,7 @@ def test_smooth():
 # Type
 
 
-def test_set_bold():
+def test_set_bold() -> None:
     instance = printer.Dummy()
     instance.set_with_default(bold=True)
 
@@ -246,7 +250,7 @@ def test_set_bold():
     assert instance.output == b"".join(expected_sequence)
 
 
-def test_set_underline():
+def test_set_underline() -> None:
     instance = printer.Dummy()
     instance.set_with_default(underline=1)
 
@@ -265,7 +269,7 @@ def test_set_underline():
     assert instance.output == b"".join(expected_sequence)
 
 
-def test_set_underline2():
+def test_set_underline2() -> None:
     instance = printer.Dummy()
     instance.set_with_default(underline=2)
 
@@ -287,7 +291,7 @@ def test_set_underline2():
 # Align
 
 
-def test_align_center():
+def test_align_center() -> None:
     instance = printer.Dummy()
     instance.set_with_default(align="center")
 
@@ -306,7 +310,7 @@ def test_align_center():
     assert instance.output == b"".join(expected_sequence)
 
 
-def test_align_right():
+def test_align_right() -> None:
     instance = printer.Dummy()
     instance.set_with_default(align="right")
 
@@ -328,7 +332,7 @@ def test_align_right():
 # Densities
 
 
-def test_densities():
+def test_densities() -> None:
     for density in range(8):
         instance = printer.Dummy()
         instance.set_with_default(density=density)
@@ -352,7 +356,7 @@ def test_densities():
 # Invert
 
 
-def test_invert():
+def test_invert() -> None:
     instance = printer.Dummy()
     instance.set_with_default(invert=True)
 

test/test_function_text.py

@@ -10,8 +10,7 @@
 
 import hypothesis.strategies as st
 import mock
-import pytest
-from hypothesis import assume, given
+from hypothesis import given
 
 from escpos.printer import Dummy
 
@@ -21,7 +20,7 @@ def get_printer():
 
 
 @given(text=st.text())
-def test_text(text):
+def test_text(text: str) -> None:
     """Test that text() calls the MagicEncode object."""
     instance = get_printer()
     instance.magic.write = mock.Mock()
@@ -29,7 +28,7 @@ def test_text(text):
     instance.magic.write.assert_called_with(text)
 
 
-def test_block_text():
+def test_block_text() -> None:
     printer = get_printer()
     printer.block_text(
         "All the presidents men were eating falafel for breakfast.", font="a"
@@ -39,25 +38,25 @@ def test_block_text():
     )
 
 
-def test_textln():
+def test_textln() -> None:
     printer = get_printer()
     printer.textln("hello, world")
     assert printer.output == b"hello, world\n"
 
 
-def test_textln_empty():
+def test_textln_empty() -> None:
     printer = get_printer()
     printer.textln()
     assert printer.output == b"\n"
 
 
-def test_ln():
+def test_ln() -> None:
     printer = get_printer()
     printer.ln()
     assert printer.output == b"\n"
 
 
-def test_multiple_ln():
+def test_multiple_ln() -> None:
     printer = get_printer()
     printer.ln(3)
     assert printer.output == b"\n\n\n"

test/test_image.py

@@ -7,11 +7,12 @@ converted to ESC/POS column & raster formats.
 :copyright: Copyright (c) 2016 `Michael Billington <michael.billington@gmail.com>`_
 :license: MIT
 """
+from typing import List
 
 from escpos.image import EscposImage
 
 
-def test_image_black():
+def test_image_black() -> None:
     """
     Test rendering solid black image
     """
@@ -19,7 +20,7 @@ def test_image_black():
         _load_and_check_img("canvas_black." + img_format, 1, 1, b"\x80", [b"\x80"])
 
 
-def test_image_black_transparent():
+def test_image_black_transparent() -> None:
     """
     Test rendering black/transparent image
     """
@@ -29,7 +30,7 @@ def test_image_black_transparent():
         )
 
 
-def test_image_black_white():
+def test_image_black_white() -> None:
     """
     Test rendering black/white image
     """
@@ -39,7 +40,7 @@ def test_image_black_white():
         )
 
 
-def test_image_white():
+def test_image_white() -> None:
     """
     Test rendering solid white image
     """
@@ -47,7 +48,7 @@ def test_image_white():
         _load_and_check_img("canvas_white." + img_format, 1, 1, b"\x00", [b"\x00"])
 
 
-def test_split():
+def test_split() -> None:
     """
     test whether the split-function works as expected
     """
@@ -62,12 +63,12 @@ def test_split():
 
 
 def _load_and_check_img(
-    filename,
-    width_expected,
-    height_expected,
-    raster_format_expected,
-    column_format_expected,
-):
+    filename: str,
+    width_expected: int,
+    height_expected: int,
+    raster_format_expected: bytes,
+    column_format_expected: List[bytes],
+) -> None:
     """
     Load an image, and test whether raster & column formatted output, sizes, etc match expectations.
     """

test/test_magicencode.py

@@ -13,7 +13,7 @@ import hypothesis.strategies as st
 import pytest
 from hypothesis import example, given
 
-from escpos.exceptions import CharCodeError, Error
+from escpos.exceptions import Error
 from escpos.katakana import encode_katakana
 from escpos.magicencode import Encoder, MagicEncode
 
@@ -23,23 +23,23 @@ class TestEncoder:
     Tests the single encoders.
     """
 
-    def test_can_encode(self):
+    def test_can_encode(self) -> None:
         assert not Encoder({"CP437": 1}).can_encode("CP437", "€")
         assert Encoder({"CP437": 1}).can_encode("CP437", "á")
         assert not Encoder({"foobar": 1}).can_encode("foobar", "a")
 
-    def test_find_suitable_encoding(self):
+    def test_find_suitable_encoding(self) -> None:
         assert not Encoder({"CP437": 1}).find_suitable_encoding("€")
         assert Encoder({"CP858": 1}).find_suitable_encoding("€") == "CP858"
 
-    def test_find_suitable_encoding_unnecessary_codepage_swap(self):
+    def test_find_suitable_encoding_unnecessary_codepage_swap(self) -> None:
         enc = Encoder({"CP857": 1, "CP437": 2, "CP1252": 3, "CP852": 4, "CP858": 5})
         # desired behavior would be that the encoder always stays in the lower
         # available codepages if possible
         for character in ("Á", "É", "Í", "Ó", "Ú"):
             assert enc.find_suitable_encoding(character) == "CP857"
 
-    def test_get_encoding(self):
+    def test_get_encoding(self) -> None:
         with pytest.raises(ValueError):
             Encoder({}).get_encoding_name("latin1")
 
@@ -122,9 +122,9 @@ class TestKatakana:
     @example("カタカナ")
     @example("あいうえお")
     @example("ﾊﾝｶｸｶﾀｶﾅ")
-    def test_accept(self, text):
+    def test_accept(self, text: str) -> None:
         encode_katakana(text)
 
-    def test_result(self):
+    def test_result(self) -> None:
         assert encode_katakana("カタカナ") == b"\xb6\xc0\xb6\xc5"
         assert encode_katakana("あいうえお") == b"\xb1\xb2\xb3\xb4\xb5"

test/test_printers/test_printer_cups.py

@@ -19,7 +19,7 @@ pytestmark = pytest.mark.skipif(
 )
 
 
-def test_device_not_initialized(cupsprinter):
+def test_device_not_initialized(cupsprinter) -> None:
     """
     GIVEN a cups printer object
     WHEN it is not initialized
@@ -28,7 +28,7 @@ def test_device_not_initialized(cupsprinter):
     assert cupsprinter._device is False
 
 
-def test_open_raise_exception(cupsprinter, devicenotfounderror):
+def test_open_raise_exception(cupsprinter, devicenotfounderror) -> None:
     """
     GIVEN a cups printer object
     WHEN open() is set to raise a DeviceNotFoundError on error
@@ -40,7 +40,7 @@ def test_open_raise_exception(cupsprinter, devicenotfounderror):
         cupsprinter.open(raise_not_found=True)
 
 
-def test_open_not_raise_exception(cupsprinter, caplog):
+def test_open_not_raise_exception(cupsprinter, caplog) -> None:
     """
     GIVEN a cups printer object
     WHEN open() is set to not raise on error but simply cancel
@@ -55,7 +55,7 @@ def test_open_not_raise_exception(cupsprinter, caplog):
     assert cupsprinter.device is None
 
 
-def test_open(cupsprinter, caplog, mocker):
+def test_open(cupsprinter, caplog, mocker) -> None:
     """
     GIVEN a cups printer object and a mocked pycups device
     WHEN a valid connection to a device is opened
@@ -74,7 +74,7 @@ def test_open(cupsprinter, caplog, mocker):
     assert cupsprinter.device
 
 
-def test_close_on_reopen(cupsprinter, mocker):
+def test_close_on_reopen(cupsprinter, mocker) -> None:
     """
     GIVEN a cups printer object and a mocked connection
     WHEN a valid connection to a device is reopened before close
@@ -112,7 +112,7 @@ def test_close(cupsprinter, caplog, mocker):
     assert cupsprinter._device is False
 
 
-def test_send_on_close(cupsprinter, mocker):
+def test_send_on_close(cupsprinter, mocker) -> None:
     """
     GIVEN a cups printer object and a mocked pycups device
     WHEN closing connection before send the buffer
@@ -133,7 +133,7 @@ def test_send_on_close(cupsprinter, mocker):
     assert cupsprinter.pending_job is False
 
 
-def test_raw_raise_exception(cupsprinter):
+def test_raw_raise_exception(cupsprinter) -> None:
     """
     GIVEN a cups printer object
     WHEN passing a non byte string to _raw()
@@ -145,7 +145,7 @@ def test_raw_raise_exception(cupsprinter):
     assert cupsprinter.pending_job is False
 
 
-def test_raw(cupsprinter):
+def test_raw(cupsprinter) -> None:
     """
     GIVEN a cups printer object
     WHEN passing a byte string to _raw()
@@ -156,7 +156,7 @@ def test_raw(cupsprinter):
     assert cupsprinter.tmpfile.read() == b"Test"
 
 
-def test_printers_no_device(cupsprinter):
+def test_printers_no_device(cupsprinter) -> None:
     """
     GIVEN a cups printer object
     WHEN device is None
@@ -166,11 +166,11 @@ def test_printers_no_device(cupsprinter):
     assert cupsprinter.printers == {}
 
 
-def test_read_no_device(cupsprinter):
+def test_read_no_device(cupsprinter) -> None:
     """
     GIVEN a cups printer object
     WHEN device is None
-    THEN check the return value is []
+    THEN check the return value is b'8'
     """
     cupsprinter.device = None
-    assert cupsprinter._read() == []
+    assert cupsprinter._read() == b"8"