DeprecationWarning with Python 3.11

[pathawks]

Describe the bug
This regular expression generates a DeprecationWarning on Python 3.11.

To Reproduce

1. Install Python 3.11
2. Run pytest
3. Observe warning

Expected behavior
No warnings.

Desktop (please complete the following information):

• OS: Ubuntu
• Version: 22.04.2 LTS

Additional context
I believe the fix should be as simple as removing the backslash. Making this change and running pytest gives me 107 passing tests and no warnings.

-                     + re.sub("[^a-z0-9_\-]", "", item.lower().replace(" ", "-"))
+                     + re.sub("[^a-z0-9_-]", "", item.lower().replace(" ", "-"))

[didix21]

Can you provide the warning?

[pathawks]

$ pytest
========================================== test session starts ===========================================
platform linux -- Python 3.11.0, pytest-7.2.2, pluggy-1.0.0
rootdir: /home/phawks/github/mdutils
collected 107 items                                                                                      

tests/test_mdutils.py .............................                                                [ 27%]
tests/test_fileutils/test_fileutils.py ........                                                    [ 34%]
tests/test_tools/test_header.py .........                                                          [ 42%]
tests/test_tools/test_html.py ...............                                                      [ 57%]
tests/test_tools/test_image.py .....                                                               [ 61%]
tests/test_tools/test_inline.py .....                                                              [ 66%]
tests/test_tools/test_mdcheckbox.py .....                                                          [ 71%]
tests/test_tools/test_mdlist.py ......                                                             [ 76%]
tests/test_tools/test_reference.py .......                                                         [ 83%]
tests/test_tools/test_table.py ....                                                                [ 86%]
tests/test_tools/test_table_of_contents.py .....                                                   [ 91%]
tests/test_tools/test_textutils.py .........                                                       [100%]

============================================ warnings summary ============================================
tests/test_mdutils.py:119
  /home/phawks/github/mdutils/tests/test_mdutils.py:119: DeprecationWarning: invalid escape sequence '\-'
    + re.sub("[^a-z0-9_\-]", "", list_headers[0].lower().replace(" ", "-"))

tests/test_mdutils.py:124
  /home/phawks/github/mdutils/tests/test_mdutils.py:124: DeprecationWarning: invalid escape sequence '\-'
    + re.sub("[^a-z0-9_\-]", "", list_headers[2].lower().replace(" ", "-"))

tests/test_mdutils.py:168
  /home/phawks/github/mdutils/tests/test_mdutils.py:168: DeprecationWarning: invalid escape sequence '\-'
    "[^a-z0-9_\-]", "", list_headers[x].lower().replace(" ", "-")

tests/test_mdutils.py:178
  /home/phawks/github/mdutils/tests/test_mdutils.py:178: DeprecationWarning: invalid escape sequence '\-'
    "[^a-z0-9_\-]", "", list_headers[x].lower().replace(" ", "-")

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
==================================== 107 passed, 4 warnings in 0.13s =====================================