Use ordinary fileno lookup in select (#9266)

* Use ordinary fileno lookup in select

Assisted-by: Codex:GPT-6

* Share select descriptor conversion

Assisted-by: Codex:GPT-6

crates/stdlib/src/select.rs

@@ -3,7 +3,8 @@
 pub(crate) use decl::module_def;
 
 use crate::vm::{
-    PyObject, PyObjectRef, PyResult, TryFromObject, VirtualMachine, builtins::PyListRef,
+    PyObject, PyObjectRef, PyResult, TryFromObject, VirtualMachine,
+    builtins::{PyInt, PyListRef},
 };
 use rustpython_host_env::select::{self as host_select, FdSet, RawFd, platform::FD_SETSIZE};
 use std::io;
@@ -17,14 +18,20 @@ struct Selectable {
 
 impl TryFromObject for Selectable {
     fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
-        let fno = obj.try_to_value(vm).or_else(|_| {
-            let meth = vm.get_method_or_type_error(
-                obj.clone(),
-                vm.ctx.interned_str("fileno").unwrap(),
-                || "select arg must be an int or object with a fileno() method".to_owned(),
-            )?;
-            meth.call((), vm)?.try_into_value(vm)
-        })?;
+        let fileno;
+        let fd = if let Some(fd) = obj.downcast_ref::<PyInt>() {
+            fd
+        } else {
+            let meth = vm.get_attribute_opt(&obj, "fileno")?.ok_or_else(|| {
+                vm.new_type_error("select arg must be an int or object with a fileno() method")
+            })?;
+            fileno = meth
+                .call((), vm)?
+                .downcast::<PyInt>()
+                .map_err(|_| vm.new_type_error("fileno() returned a non-integer"))?;
+            &fileno
+        };
+        let fno = fd.try_to_primitive(vm)?;
         Ok(Self { obj, fno })
     }
 }

extra_tests/snippets/stdlib_select.py

@@ -167,3 +167,35 @@ if hasattr(select, "poll") and hasattr(signal, "setitimer"):
     assert handled == [signal.SIGALRM], handled
     idle.close()
     idle_peer.close()
+
+
+# fileno is an ordinary attribute, not a special method.
+class InstanceFileno:
+    pass
+
+
+class DynamicFileno:
+    def __getattr__(self, name):
+        if name == "fileno":
+            return lookup_reader.fileno
+        raise AttributeError(name)
+
+
+class IndexOnly:
+    def __index__(self):
+        return lookup_reader.fileno()
+
+
+lookup_reader, lookup_writer = socket.socketpair()
+try:
+    lookup_writer.send(b"x")
+    instance = InstanceFileno()
+    instance.fileno = lookup_reader.fileno
+    for obj in (instance, DynamicFileno()):
+        assert select.select([obj], [], [], 0) == ([obj], [], [])
+    assert_raises(TypeError, select.select, [IndexOnly()], [], [], 0)
+    instance.fileno = IndexOnly
+    assert_raises(TypeError, select.select, [instance], [], [], 0)
+finally:
+    lookup_reader.close()
+    lookup_writer.close()