API client generator template uses deprecated syntax for regular expressions

[jkachel]

Description

Using the REST Client library in a project with Python >= 3.12 results in chattery SyntaxWarning messages, and sometimes pytest failures.

Starting in Python 3.6, strings that contain invalid escape sequences raise a DeprecationWarning. This includes regular strings that are used for regex expressions, as regex uses backslashed characters to denote operators/classes/etc. and those don't match up with escape sequences. DeprecationWarning is usually silent, but in 3.12 this was changed so that these now emit a SyntaxWarning, which isn't silent.

Compounding the issue is that pytest treats these as a failure when using Python 3.13.

More Info

The change is noted in the What's New for 3.12 here: https://docs.python.org/3/whatsnew/3.12.html#other-language-changes

See also the discussion here: python/cpython#98401

I created a very simple test case that demonstrates the issue. It is available here: https://github.com/jkachel/cybersource-rest-error

The pytest error output is in a comment below to keep this issue from being too long.

Potential Fix

Regular expressions should use raw strings.

The main offenders seem to be here:

cybersource-rest-client-python/generator/cybersource-python-template/api_client.mustache

Line 424 in 9d057e3

sub_kls = re.match('list\[(.*)\]', klass).group(1)

and in line 429 in the same file. The fix should be as simple as adding r to the start of those regex strings. I don't have a workflow set up for regenerating this client, and there may be other instances where this should be fixed that I don't know about, so I haven't tried to fix it.

Workaround

Client code can use the warnings library to filter SyntaxWarning when importing the CyberSource API client. Ex:

import warnings

with warnings.catch_warnings():
	warnings.filterwarnings("ignore", category=SyntaxWarning)
	from CyberSource import ApiClient, OrdersApi

This resolves the issue in the short term but these should be fixed - as noted in the change, Python will (eventually) start emitting SyntaxError for these issues.

[jkachel]

Pytest output (note that this is actually when running 3.12):

$ uv run --python 3.13 pytest
Using CPython 3.13.0
Removed virtual environment at: .venv
Creating virtual environment at: .venv
Installed 19 packages in 65ms
==================================================== test session starts ====================================================
platform darwin -- Python 3.13.0, pytest-8.3.4, pluggy-1.5.0
rootdir: /Users/jkachel/src/cybersource-error
configfile: pytest.ini
collected 0 items / 1 error

========================================================== ERRORS ===========================================================
______________________________________________ ERROR collecting index_test.py _______________________________________________
.venv/lib/python3.13/site-packages/_pytest/python.py:493: in importtestmodule
    mod = import_path(
.venv/lib/python3.13/site-packages/_pytest/pathlib.py:587: in import_path
    importlib.import_module(module_name)
../../.local/share/uv/python/cpython-3.13.0-macos-aarch64-none/lib/python3.13/importlib/__init__.py:88: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
<frozen importlib._bootstrap>:1387: in _gcd_import
    ???
<frozen importlib._bootstrap>:1360: in _find_and_load
    ???
<frozen importlib._bootstrap>:1331: in _find_and_load_unlocked
    ???
<frozen importlib._bootstrap>:935: in _load_unlocked
    ???
.venv/lib/python3.13/site-packages/_pytest/assertion/rewrite.py:184: in exec_module
    exec(co, module.__dict__)
index_test.py:5: in <module>
    from index import create_orders_api
index.py:3: in <module>
    from CyberSource import ApiClient, OrdersApi
.venv/lib/python3.13/site-packages/CyberSource/__init__.py:1386: in <module>
    from .api.o_auth_api import OAuthApi
.venv/lib/python3.13/site-packages/CyberSource/api/__init__.py:4: in <module>
    from .o_auth_api import OAuthApi
.venv/lib/python3.13/site-packages/CyberSource/api/o_auth_api.py:24: in <module>
    from ..api_client import ApiClient
E     File "/Users/jkachel/src/cybersource-error/.venv/lib/python3.13/site-packages/CyberSource/api_client.py", line 432
E       sub_kls = re.match('list\[(.*)\]', klass).group(1)
E                          ^^^^^^^^^^^^^^
E   SyntaxError: invalid escape sequence '\['
================================================== short test summary info ==================================================
ERROR index_test.py
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
===================================================== 1 error in 1.63s ======================================================