parent: handle masters with blank sys.executable; closes #356.

docs/changelog.rst

@@ -174,6 +174,11 @@ Core Library
 * `#345 <https://github.com/dw/mitogen/issues/345>`_: the SSH connection method
   allows optionally disabling ``IdentitiesOnly yes``.
 
+* `#356 <https://github.com/dw/mitogen/issues/356>`_: if the master Python
+  process does not have :data:`sys.executable` set, the default Python
+  interpreter used for new children on the local machine defaults to
+  ``"/usr/bin/python"``.
+
 * `#366 <https://github.com/dw/mitogen/issues/366>`_,
   `#380 <https://github.com/dw/mitogen/issues/380>`_: attempts by children to
   import :mod:`__main__` where the main program module lacks an execution guard

mitogen/fakessh.py

@@ -436,7 +436,7 @@ def run(dest, router, args, deadline=None, econtext=None):
         ssh_path = os.path.join(tmp_path, 'ssh')
         fp = open(ssh_path, 'w')
         try:
-            fp.write('#!%s\n' % (sys.executable,))
+            fp.write('#!%s\n' % (mitogen.parent.get_sys_executable(),))
             fp.write(inspect.getsource(mitogen.core))
             fp.write('\n')
             fp.write('ExternalContext(%r).main()\n' % (
@@ -449,7 +449,7 @@ def run(dest, router, args, deadline=None, econtext=None):
         env = os.environ.copy()
         env.update({
             'PATH': '%s:%s' % (tmp_path, env.get('PATH', '')),
-            'ARGV0': sys.executable,
+            'ARGV0': mitogen.parent.get_sys_executable(),
             'SSH_PATH': ssh_path,
         })
 

mitogen/parent.py

@@ -85,11 +85,35 @@ OPENPTY_MSG = (
     "to avoid PTY use."
 )
 
+SYS_EXECUTABLE_MSG = (
+    "The Python sys.executable variable is unset, indicating Python was "
+    "unable to determine its original program name. Unless explicitly "
+    "configured otherwise, child contexts will be started using "
+    "'/usr/bin/python'"
+)
+_sys_executable_warning_logged = False
+
 
 def get_log_level():
     return (LOG.level or logging.getLogger().level or logging.INFO)
 
 
+def get_sys_executable():
+    """
+    Return :data:`sys.executable` if it is set, otherwise return
+    ``"/usr/bin/python"`` and log a warning.
+    """
+    if sys.executable:
+        return sys.executable
+
+    global _sys_executable_warning_logged
+    if not _sys_executable_warning_logged:
+        LOG.warn(SYS_EXECUTABLE_MSG)
+        _sys_executable_warning_logged = True
+
+    return '/usr/bin/python'
+
+
 def get_core_source():
     """
     In non-masters, simply fetch the cached mitogen.core source code via the
@@ -841,7 +865,7 @@ class Stream(mitogen.core.Stream):
     Base for streams capable of starting new slaves.
     """
     #: The path to the remote Python interpreter.
-    python_path = sys.executable
+    python_path = get_sys_executable()
 
     #: Maximum time to wait for a connection attempt.
     connect_timeout = 30.0