Preliminary Python 3.13 compatibility (#513)

* Preliminary Python 3.13 compatibility

* CI: add a Python 3.13 job

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-20.04, ubuntu-22.04, macos-12, macos-14]
-        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]
 
     steps:
     - uses: actions/checkout@v4

argcomplete/packages/_argparse.py

@@ -5,6 +5,7 @@
 
 # This file contains argparse introspection utilities used in the course of argcomplete execution.
 
+import sys
 from argparse import (
     ONE_OR_MORE,
     OPTIONAL,
@@ -15,6 +16,7 @@
     Action,
     ArgumentError,
     ArgumentParser,
+    Namespace,
     _get_action_name,
     _SubParsersAction,
 )
@@ -75,6 +77,19 @@ class IntrospectiveArgumentParser(ArgumentParser):
     except for the lines that contain the string "Added by argcomplete".
     '''
 
+    def _parse_known_args2(self, args, namespace, intermixed):
+        if args is None:
+            # args default to the system args
+            args = sys.argv[1:]
+        else:
+            # make sure that args are mutable
+            args = list(args)
+
+        # default Namespace built from parser defaults
+        if namespace is None:
+            namespace = Namespace()
+        return self._parse_known_args(args, namespace)
+
     def _parse_known_args(self, arg_strings, namespace):
         _num_consumed_args.clear()  # Added by argcomplete
         self._argcomplete_namespace = namespace