The docs for the acquire method in both the thread and
threading modules are incorrect.  They describe an old
(insane) version that returned None when called with no
argument. It appears that acquire is now sane, and
always returns True or False.

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It certainly seems that there is a code path in Lock.acquire
that can return None, as the following excerpt from
Modules/threadmodule.c shows:

static PyObject *
lock_PyThread_acquire_lock(lockobject *self, PyObject *args)
{
   int i = 1;

   if (!PyArg_ParseTuple(args, "|i:acquire", &i))
      return NULL;

   Py_BEGIN_ALLOW_THREADS
   i = PyThread_acquire_lock(self->lock_lock, i);
   Py_END_ALLOW_THREADS

   if (args == NULL) {
      Py_INCREF(Py_None);
      return Py_None;
   }
   else
      return PyBool_FromLong((long)i);
}

Nevertheless, a_lock.acquire() still returns true.

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I think the (args==NULL) code path is vestigial and can no longer be 
executed, because the PyArg_ParseTuple call will fail if args is NULL.

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I've changed the docs on both the HEAD and 2.4-maint branches to only 
describe the True/False return values.  Thanks for your report!