youknowone · May 13, 2026 · May 5, 2026 · May 5, 2026 · May 5, 2026 · May 5, 2026
diff --git a/.cspell.dict/cpython.txt b/.cspell.dict/cpython.txt
@@ -157,6 +157,7 @@ pybuilddir
 pycore
 pyinner
 pydecimal
+pyerrors
 Pyfunc
 pylifecycle
 pymain

diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
@@ -112,10 +112,15 @@ jobs:
         uses: ./.github/actions/install-macos-deps
 
       - name: run rust tests
-        run: cargo test --workspace ${{ env.WORKSPACE_EXCLUDES }} --features threading ${{ env.CARGO_ARGS }}
+        run: cargo test --workspace --exclude rustpython-capi ${{ env.WORKSPACE_EXCLUDES }} --features threading ${{ env.CARGO_ARGS }}
         env:
           INSTA_WORKSPACE_ROOT: ${{ github.workspace }}
 
+      - name: run c-api tests
+        working-directory: crates/capi
+        run: cargo test
+        if: runner.os != 'Windows'  # Requires pyo3 0.29+ on Windows
+
       - run: cargo doc --locked
         if: runner.os == 'Linux'
 

diff --git a/crates/capi/src/lib.rs b/crates/capi/src/lib.rs
@@ -1,19 +1,33 @@
 #![allow(clippy::missing_safety_doc)]
 
+use crate::pyerrors::init_exception_statics;
 use crate::pylifecycle::MAIN_INTERP;
-use rustpython_vm::Interpreter;
 pub use rustpython_vm::PyObject;
+use rustpython_vm::{Context, Interpreter};
 use std::sync::MutexGuard;
 
 extern crate alloc;
 
+pub mod object;
+pub mod pyerrors;
 pub mod pylifecycle;
 pub mod pystate;
 pub mod refcount;
+mod util;
 
 /// Get main interpreter of this process. Will be None if it has not been initialized yet.
 pub fn get_main_interpreter() -> MutexGuard<'static, Option<Interpreter>> {
     MAIN_INTERP
         .lock()
         .expect("Failed to lock interpreter mutex")
 }
+
+/// Set the main interpreter of this process. This method will panic when there is already an
+/// interpreter set.
+pub fn set_main_interpreter(interpreter: Interpreter) {
+    let mut interp = get_main_interpreter();
+    assert!(interp.is_none(), "Main interpreter is already set");
+    // Safety: Interpreter was not initialized before, so we can safely assume the statics are not used
+    unsafe { init_exception_statics(&Context::genesis().exceptions) };
+    *interp = Some(interpreter);
+}
diff --git a/crates/capi/src/object.rs b/crates/capi/src/object.rs
@@ -0,0 +1,88 @@
+use crate::PyObject;
+use crate::pystate::with_vm;
+use core::ffi::{c_int, c_uint, c_ulong};
+use rustpython_vm::builtins::PyType;
+use rustpython_vm::{AsObject, Context, Py};
+
+const PY_TPFLAGS_LONG_SUBCLASS: u64 = 1 << 24;
+const PY_TPFLAGS_LIST_SUBCLASS: u64 = 1 << 25;
+const PY_TPFLAGS_TUPLE_SUBCLASS: u64 = 1 << 26;
+const PY_TPFLAGS_BYTES_SUBCLASS: u64 = 1 << 27;
+const PY_TPFLAGS_UNICODE_SUBCLASS: u64 = 1 << 28;
+const PY_TPFLAGS_DICT_SUBCLASS: u64 = 1 << 29;
+const PY_TPFLAGS_BASE_EXC_SUBCLASS: u64 = 1 << 30;
+const PY_TPFLAGS_TYPE_SUBCLASS: u64 = 1 << 31;
+
+pub type PyTypeObject = Py<PyType>;
+
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn Py_TYPE(op: *mut PyObject) -> *const PyTypeObject {
+    unsafe { (*op).class() }
+}
+
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn Py_IS_TYPE(op: *mut PyObject, ty: *mut PyTypeObject) -> c_int {
+    with_vm(|_vm| {
+        let obj = unsafe { &*op };
+        let ty = unsafe { &*ty };
+        obj.class().is(ty)
+    })
+}
+
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn PyType_GetFlags(ptr: *const PyTypeObject) -> c_ulong {
+    let ctx = Context::genesis();
+    let zoo = &ctx.types;
+    let exp_zoo = &ctx.exceptions;
+
+    let ty = unsafe { &*ptr };
+    let mut flags = ty.slots.flags.bits();
+
+    if ty.is_subtype(zoo.int_type) {
+        flags |= PY_TPFLAGS_LONG_SUBCLASS;
+    }
+    if ty.is_subtype(zoo.list_type) {
+        flags |= PY_TPFLAGS_LIST_SUBCLASS
+    }
+    if ty.is_subtype(zoo.tuple_type) {
+        flags |= PY_TPFLAGS_TUPLE_SUBCLASS;
+    }
+    if ty.is_subtype(zoo.bytes_type) {
+        flags |= PY_TPFLAGS_BYTES_SUBCLASS;
+    }
+    if ty.is_subtype(zoo.str_type) {
+        flags |= PY_TPFLAGS_UNICODE_SUBCLASS;
+    }
+    if ty.is_subtype(zoo.dict_type) {
+        flags |= PY_TPFLAGS_DICT_SUBCLASS;
+    }
+    if ty.is_subtype(exp_zoo.base_exception_type) {
+        flags |= PY_TPFLAGS_BASE_EXC_SUBCLASS;
+    }
+    if ty.is_subtype(zoo.type_type) {
+        flags |= PY_TPFLAGS_TYPE_SUBCLASS;
+    }
+
+    flags as c_ulong
+}
+
+#[unsafe(no_mangle)]
+pub extern "C" fn Py_GetConstantBorrowed(constant_id: c_uint) -> *mut PyObject {
+    with_vm(|vm| {
+        let ctx = &vm.ctx;
+        let constant = match constant_id {
+            0 => ctx.none.as_object(),
+            1 => ctx.false_value.as_object(),
+            2 => ctx.true_value.as_object(),
+            3 => ctx.ellipsis.as_object(),
+            4 => ctx.not_implemented.as_object(),
+            _ => {
+                return Err(
+                    vm.new_system_error("Invalid constant ID passed to Py_GetConstantBorrowed")
+                );
+            }
+        }
+        .as_raw();
+        Ok(constant)
+    })
+}
-Original file line number
+Diff line change
@@ Expand Up / @@ -157,6 +157,7 @@ pybuilddir @@
     pycore
     pyinner
     pydecimal
+    pyerrors
     Pyfunc
     pylifecycle
     pymain
@@ Expand Down @@