DeprecationWarning: codecs.open() is deprecated in Python 3.13+

[Vallhalen]

Description

When running tests with Python 3.12+, the library emits deprecation warnings about codecs.open():

DeprecationWarning: 'codecs.open' is deprecated. Use built-in open() instead.

This appears to come from the internal file loading mechanism.

Environment

• Python: 3.12+
• python-frontmatter: 1.1.0

Suggested Fix

Replace codecs.open() with the built-in open() function with explicit encoding parameter:

# Before
import codecs
with codecs.open(path, 'r', encoding='utf-8') as f:
    content = f.read()

# After
with open(path, 'r', encoding='utf-8') as f:
    content = f.read()

The built-in open() has supported the encoding parameter since Python 3.0, so this change would be backwards compatible.

Workaround

Currently filtering the warning in pytest.ini:

filterwarnings =
    ignore::DeprecationWarning:frontmatter.*:

Thank you for maintaining this library!