youknowone · Oct 31, 2026 · Oct 30, 2026 · Oct 30, 2026
diff --git a/Lib/test/test_cmd_line.py b/Lib/test/test_cmd_line.py
@@ -728,7 +728,6 @@ def test_isolatedmode(self):
                                           cwd=tmpdir)
             self.assertEqual(out.strip(), b"ok")
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON
     def test_sys_flags_set(self):
         # Issue 31845: a startup refactoring broke reading flags from env vars
         for value, expected in (("", 0), ("1", 1), ("text", 1), ("2", 2)):
@@ -750,7 +749,6 @@ def test_sys_flags_set(self):
             with self.subTest(envar_value=value):
                 assert_python_ok('-c', code, **env_vars)
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON
     def test_set_pycache_prefix(self):
         # sys.pycache_prefix can be set from either -X pycache_prefix or
         # PYTHONPYCACHEPREFIX env var, with the former taking precedence.

diff --git a/Lib/test/test_compileall.py b/Lib/test/test_compileall.py
@@ -598,7 +598,6 @@ def assertNotCompiled(self, fn):
         path = importlib.util.cache_from_source(fn)
         self.assertFalse(os.path.exists(path))
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON
     def test_no_args_compiles_path(self):
         # Note that -l is implied for the no args case.
         bazfn = script_helper.make_script(self.directory, 'baz', '')
@@ -608,7 +607,6 @@ def test_no_args_compiles_path(self):
             self.assertNotCompiled(self.initfn)
             self.assertNotCompiled(self.barfn)
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON
     @without_source_date_epoch  # timestamp invalidation test
     @support.requires_resource('cpu')
     def test_no_args_respects_force_flag(self):

diff --git a/crates/vm/src/stdlib/sys.rs b/crates/vm/src/stdlib/sys.rs
@@ -733,8 +733,13 @@ pub mod sys {
     }
 
     #[pyattr]
-    fn pycache_prefix(vm: &VirtualMachine) -> PyObjectRef {
-        vm.ctx.none()
+    fn pycache_prefix(vm: &VirtualMachine) -> Option<PyStrRef> {
+        vm.state
+            .config
+            .settings
+            .pycache_prefix
+            .clone()
+            .map(|value| vm.fsdecode(value))
     }
 
     #[pyattr(name = "version")]

diff --git a/crates/vm/src/vm/setting.rs b/crates/vm/src/vm/setting.rs
@@ -1,5 +1,4 @@
 use core::num::NonZeroI32;
-#[cfg(feature = "flame-it")]
 use std::ffi::OsString;
 
 /// Path configuration computed at runtime (like PyConfig path outputs)
@@ -74,7 +73,8 @@ pub struct Settings {
     // int malloc_stats;
     // wchar_t *filesystem_encoding;
     // wchar_t *filesystem_errors;
-    // wchar_t *pycache_prefix;
+    /// -X pycache_prefix, PYTHONPYCACHEPREFIX
+    pub pycache_prefix: Option<OsString>,
     // int parse_argv;
     // PyWideStringList orig_argv;
     /// sys.argv
@@ -230,6 +230,7 @@ impl Default for Settings {
             hash_seed: None,
             faulthandler: false,
             import_time: 0,
+            pycache_prefix: None,
             code_debug_ranges: true,
             buffered_stdio: true,
             check_hash_pycs_mode: CheckHashPycsMode::Default,

diff --git a/src/settings.rs b/src/settings.rs
@@ -253,7 +253,7 @@ pub fn parse_opts() -> Result<(Settings, RunMode), lexopt::Error> {
 
     settings.optimize = cmp::max(args.optimize, env_count("PYTHONOPTIMIZE"));
     settings.verbose = cmp::max(args.verbose, env_count("PYTHONVERBOSE"));
-    settings.debug = cmp::max(args.debug, env_count("PYTHONDEBUG"));
+    settings.debug = u8::from(cmp::max(args.debug, env_count("PYTHONDEBUG")) != 0);
 
     let env_bool = |env| get_env(env).is_some_and(|v| !v.is_empty());
     settings.dev_mode = env_bool("PYTHONDEVMODE");
@@ -295,6 +295,7 @@ pub fn parse_opts() -> Result<(Settings, RunMode), lexopt::Error> {
     }
 
     settings.check_hash_pycs_mode = args.check_hash_based_pycs;
+    settings.pycache_prefix = get_env("PYTHONPYCACHEPREFIX").filter(|value| !value.is_empty());
 
     if let Some(val) = get_env("PYTHON_LAZY_IMPORTS").filter(|val| !val.is_empty()) {
         settings.lazy_imports = parse_lazy_imports(val.to_str(), "PYTHON_LAZY_IMPORTS");
@@ -314,13 +315,18 @@ pub fn parse_opts() -> Result<(Settings, RunMode), lexopt::Error> {
     let mut import_time_option_seen = false;
     let mut frozen_modules_option_seen = false;
     let mut utf8_option_seen = false;
+    let mut pycache_prefix_option_seen = false;
     let xopts = args.implementation_option.into_iter().map(|s| {
         let (name, value) = match s.split_once('=') {
             Some((name, value)) => (name.to_owned(), Some(value)),
             None => (s, None),
         };
         match &*name {
             "dev" => settings.dev_mode = true,
+            "pycache_prefix" if !pycache_prefix_option_seen => {
+                settings.pycache_prefix = value.filter(|value| !value.is_empty()).map(Into::into);
+                pycache_prefix_option_seen = true;
+            }
             "importtime" if !import_time_option_seen => {
                 settings.import_time = parse_import_time(value, "-X importtime");
                 import_time_option_seen = true;