ansible_mitogen: Use INTERPRETER_PYTHON_FALLBACK as python candidates

This shouldn't change the interpreter ultimately chosen by Ansible. It should
only improve the hit rate of performing interpreter discovery, particular in
cases where only pythonX.Y is present on the target.

Interpreter discovery may take longer or shorter, depending on the Ansible
version and the interpreters present on the target.

Author: moreati

ansible_mitogen/mixins.py

@@ -470,18 +470,7 @@ def _low_level_execute_command(self, cmd, sudoable=True, in_data=None,
         # chicken-and-egg issue, mitogen needs a python to run low_level_execute_command
         # which is required by Ansible's discover_interpreter function
         if self._mitogen_discovering_interpreter:
-            possible_pythons = [
-                '/usr/bin/python',
-                'python3',
-                'python3.7',
-                'python3.6',
-                'python3.5',
-                'python2.7',
-                'python2.6',
-                '/usr/libexec/platform-python',
-                '/usr/bin/python3',
-                'python'
-            ]
+            possible_pythons = self._mitogen_interpreter_candidates
         else:
             # not used, just adding a filler value
             possible_pythons = ['python']
@@ -492,12 +481,15 @@ def _low_level_execute_command(self, cmd, sudoable=True, in_data=None,
                 rc, stdout, stderr = self._connection.exec_command(
                     cmd, in_data, sudoable, mitogen_chdir=chdir,
                 )
-            # TODO: what exception is thrown?
-            except:
+            except BaseException as exc:
                 # we've reached the last python attempted and failed
                 if possible_python == possible_pythons[-1]:
                     raise
                 else:
+                    LOG.debug(
+                        '%r._low_level_execute_command: candidate=%r ignored: %s, %r',
+                        self, possible_python, type(exc), exc,
+                    )
                     continue
 
         stdout_text = to_text(stdout, errors=encoding_errors)

ansible_mitogen/transport_config.py

@@ -73,13 +73,21 @@
 from ansible.module_utils.six import with_metaclass
 from ansible.module_utils.parsing.convert_bool import boolean
 
+import ansible_mitogen.utils
 import mitogen.core
 
 
 LOG = logging.getLogger(__name__)
 
+if ansible_mitogen.utils.ansible_version[:2] >= (2, 19):
+    _FALLBACK_INTERPRETER = ansible.executor.interpreter_discovery._FALLBACK_INTERPRETER
+elif ansible_mitogen.utils.ansible_version[:2] >= (2, 17):
+    _FALLBACK_INTERPRETER = u'/usr/bin/python3'
+else:
+    _FALLBACK_INTERPRETER = u'/usr/bin/python'
 
-def run_interpreter_discovery_if_necessary(s, task_vars, action, rediscover_python):
+
+def run_interpreter_discovery_if_necessary(s, candidates, task_vars, action, rediscover_python):
     """
     Triggers ansible python interpreter discovery if requested.
     Caches this value the same way Ansible does it.
@@ -107,8 +115,11 @@ def run_interpreter_discovery_if_necessary(s, task_vars, action, rediscover_pyth
             # blow away the discovered_interpreter_config cache and rediscover
             del task_vars['ansible_facts'][discovered_interpreter_config]
 
-        if discovered_interpreter_config not in task_vars['ansible_facts']:
+        try:
+            s = task_vars[u'ansible_facts'][discovered_interpreter_config]
+        except KeyError:
             action._mitogen_discovering_interpreter = True
+            action._mitogen_interpreter_candidates = candidates
             # fake pipelining so discover_interpreter can be happy
             action._connection.has_pipelining = True
             s = ansible.executor.interpreter_discovery.discover_interpreter(
@@ -121,18 +132,17 @@ def run_interpreter_discovery_if_necessary(s, task_vars, action, rediscover_pyth
             # cache discovered interpreter
             task_vars['ansible_facts'][discovered_interpreter_config] = s
             action._connection.has_pipelining = False
-        else:
-            s = task_vars['ansible_facts'][discovered_interpreter_config]
 
         # propagate discovered interpreter as fact
         action._discovered_interpreter_key = discovered_interpreter_config
         action._discovered_interpreter = s
 
     action._mitogen_discovering_interpreter = False
+    action._mitogen_interpreter_candidates = None
     return s
 
 
-def parse_python_path(s, task_vars, action, rediscover_python):
+def parse_python_path(s, candidates, task_vars, action, rediscover_python):
     """
     Given the string set for ansible_python_interpeter, parse it using shell
     syntax and return an appropriate argument vector. If the value detected is
@@ -143,10 +153,9 @@ def parse_python_path(s, task_vars, action, rediscover_python):
         # if python_path doesn't exist, default to `auto` and attempt to discover it
         s = 'auto'
 
-    s = run_interpreter_discovery_if_necessary(s, task_vars, action, rediscover_python)
-    # if unable to determine python_path, fallback to '/usr/bin/python'
+    s = run_interpreter_discovery_if_necessary(s, candidates, task_vars, action, rediscover_python)
     if not s:
-        s = '/usr/bin/python'
+        s = _FALLBACK_INTERPRETER
 
     return ansible.utils.shlex.shlex_split(s)
 
@@ -510,13 +519,17 @@ def python_path(self, rediscover_python=False):
         interpreter_python = C.config.get_config_value(
             'INTERPRETER_PYTHON', variables=variables,
         )
+        interpreter_python_fallback = C.config.get_config_value(
+            'INTERPRETER_PYTHON_FALLBACK', variables=variables,
+        )
 
         if '{{' in interpreter_python or '{%' in interpreter_python:
             templar = self._connection.templar
             interpreter_python = templar.template(interpreter_python)
 
         return parse_python_path(
             interpreter_python,
+            candidates=interpreter_python_fallback,
             task_vars=self._task_vars,
             action=self._action,
             rediscover_python=rediscover_python)
@@ -732,11 +745,12 @@ def port(self):
 
     def python_path(self, rediscover_python=False):
         s = self._host_vars.get('ansible_python_interpreter')
-        # #511, #536: executor/module_common.py::_get_shebang() hard-wires
-        # "/usr/bin/python" as the default interpreter path if no other
-        # interpreter is specified.
+        interpreter_python_fallback = self._host_vars.get(
+            'ansible_interpreter_python_fallback', [],
+        )
         return parse_python_path(
             s,
+            candidates=interpreter_python_fallback,
             task_vars=self._task_vars,
             action=self._action,
             rediscover_python=rediscover_python)

docs/changelog.rst

@@ -21,6 +21,9 @@ To avail of fixes in an unreleased version, please download a ZIP file
 In progress (unreleased)
 ------------------------
 
+* :gh:issue:`1132` :mod:`ansible_mitogen` During intrepreter discovery use
+  Ansible ``INTERPRETER_PYTHON_FALLBACK`` config as list of candidates
+
 
 v0.3.34 (2025-11-27)
 --------------------