From 4e85229f641a2ebe65c7d07af84e76ac6b0b8adc Mon Sep 17 00:00:00 2001
From: Ethan Sarp <11684270+esarp@users.noreply.github.com>
Date: Fri, 19 Dec 2025 16:02:31 -0600
Subject: [PATCH 1/3] [mypyc] Implement bytes.endswith

---
 mypyc/lib-rt/CPy.h                 |  2 +-
 mypyc/lib-rt/bytes_ops.c           | 38 ++++++++++++++++++++++++++++++
 mypyc/primitives/bytes_ops.py      | 10 ++++++++
 mypyc/test-data/fixtures/ir.py     |  2 ++
 mypyc/test-data/irbuild-bytes.test | 13 ++++++++++
 mypyc/test-data/run-bytes.test     | 21 +++++++++++++++++
 6 files changed, 85 insertions(+), 1 deletion(-)

diff --git a/mypyc/lib-rt/CPy.h b/mypyc/lib-rt/CPy.h
index 68c0be2bd748..af5247e64393 100644
--- a/mypyc/lib-rt/CPy.h
+++ b/mypyc/lib-rt/CPy.h
@@ -790,7 +790,7 @@ PyObject *CPyBytes_Join(PyObject *sep, PyObject *iter);
 CPyTagged CPyBytes_Ord(PyObject *obj);
 PyObject *CPyBytes_Multiply(PyObject *bytes, CPyTagged count);
 int CPyBytes_Startswith(PyObject *self, PyObject *subobj);
-
+int CPyBytes_Endswith(PyObject *self, PyObject *subobj);
 int CPyBytes_Compare(PyObject *left, PyObject *right);
 
 
diff --git a/mypyc/lib-rt/bytes_ops.c b/mypyc/lib-rt/bytes_ops.c
index 2a03e32a013a..9552e54ff5ce 100644
--- a/mypyc/lib-rt/bytes_ops.c
+++ b/mypyc/lib-rt/bytes_ops.c
@@ -183,3 +183,41 @@ int CPyBytes_Startswith(PyObject *self, PyObject *subobj) {
     }
     return ret;
 }
+
+int CPyBytes_Endswith(PyObject *self, PyObject *subobj) {
+    if (PyBytes_CheckExact(self) && PyBytes_CheckExact(subobj)) {
+        if (self == subobj) {
+            return 1;
+        }
+
+        Py_ssize_t subobj_len = PyBytes_GET_SIZE(subobj);
+        if (subobj_len == 0) {
+            return 1;
+        }
+
+        Py_ssize_t self_len = PyBytes_GET_SIZE(self);
+        if (subobj_len > self_len) {
+            return 0;
+        }
+
+        const char *self_buf = PyBytes_AS_STRING(self);
+        const char *subobj_buf = PyBytes_AS_STRING(subobj);
+
+        return memcmp(self_buf + (self_len - subobj_len), subobj_buf, (size_t)subobj_len) == 0 ? 1 : 0;
+    }
+    _Py_IDENTIFIER(endswith);
+    PyObject *name = _PyUnicode_FromId(&PyId_endswith);
+    if (name == NULL) {
+        return 2;
+    }
+    PyObject *result = PyObject_CallMethodOneArg(self, name, subobj);
+    if (result == NULL) {
+        return 2;
+    }
+    int ret = PyObject_IsTrue(result);
+    Py_DECREF(result);
+    if (ret < 0) {
+        return 2;
+    }
+    return ret;
+}
diff --git a/mypyc/primitives/bytes_ops.py b/mypyc/primitives/bytes_ops.py
index 0b32c7937ba1..5775bcda6469 100644
--- a/mypyc/primitives/bytes_ops.py
+++ b/mypyc/primitives/bytes_ops.py
@@ -133,6 +133,16 @@
     error_kind=ERR_MAGIC,
 )
 
+# bytes.endswith(bytes)
+method_op(
+    name="endswith",
+    arg_types=[bytes_rprimitive, bytes_rprimitive],
+    return_type=c_int_rprimitive,
+    c_function_name="CPyBytes_Endswith",
+    truncated_type=bool_rprimitive,
+    error_kind=ERR_MAGIC,
+)
+
 # Join bytes objects and return a new bytes.
 # The first argument is the total number of the following bytes.
 bytes_build_op = custom_op(
diff --git a/mypyc/test-data/fixtures/ir.py b/mypyc/test-data/fixtures/ir.py
index c608a68c26e9..c21eeca9d2fe 100644
--- a/mypyc/test-data/fixtures/ir.py
+++ b/mypyc/test-data/fixtures/ir.py
@@ -180,6 +180,7 @@ def join(self, x: Iterable[object]) -> bytes: ...
     def decode(self, encoding: str=..., errors: str=...) -> str: ...
     def translate(self, t: bytes | bytearray) -> bytes: ...
     def startswith(self, t: bytes | bytearray) -> bool: ...
+    def endswith(self, t: bytes | bytearray) -> bool: ...
     def __iter__(self) -> Iterator[int]: ...
 
 class bytearray:
@@ -197,6 +198,7 @@ def __getitem__(self, i: int) -> int: ...
     def __getitem__(self, i: slice) -> bytearray: ...
     def decode(self, x: str = ..., y: str = ...) -> str: ...
     def startswith(self, t: bytes) -> bool: ...
+    def endswith(self, t: bytes) -> bool: ...
 
 class bool(int):
     def __init__(self, o: object = ...) -> None: ...
diff --git a/mypyc/test-data/irbuild-bytes.test b/mypyc/test-data/irbuild-bytes.test
index 391be56f00d2..c03bcf5d2067 100644
--- a/mypyc/test-data/irbuild-bytes.test
+++ b/mypyc/test-data/irbuild-bytes.test
@@ -266,6 +266,19 @@ L0:
     r1 = truncate r0: i32 to builtins.bool
     return r1
 
+[case testBytesEndsWith]
+def f(a: bytes, b: bytes) -> bool:
+    return a.endswith(b)
+[out]
+def f(a, b):
+    a, b :: bytes
+    r0 :: i32
+    r1 :: bool
+L0:
+    r0 = CPyBytes_Endswith(a, b)
+    r1 = truncate r0: i32 to builtins.bool
+    return r1
+
 [case testBytesVsBytearray]
 def bytes_func(b: bytes) -> None: pass
 def bytearray_func(ba: bytearray) -> None: pass
diff --git a/mypyc/test-data/run-bytes.test b/mypyc/test-data/run-bytes.test
index 89ccfd66d288..afb863a3b350 100644
--- a/mypyc/test-data/run-bytes.test
+++ b/mypyc/test-data/run-bytes.test
@@ -221,6 +221,27 @@ def test_startswith() -> None:
     assert test2.startswith(b'some')
     assert not test2.startswith(b'other')
 
+def test_endswith() -> None:
+    # Test default behavior
+    test = b'some string'
+    assert test.endswith(b'string')
+    assert test.endswith(b'some string')
+    assert not test.endswith(b'other')
+    assert not test.endswith(b'some string but longer')
+
+    # Test empty cases
+    assert test.endswith(b'')
+    assert b''.endswith(b'')
+    assert not b''.endswith(test)
+
+    # Test bytearray to verify slow paths
+    assert test.endswith(bytearray(b'string'))
+    assert not test.endswith(bytearray(b'other'))
+
+    test = bytearray(b'some string')
+    assert test.endswith(b'string')
+    assert not test.endswith(b'other')
+
 [case testBytesSlicing]
 def test_bytes_slicing() -> None:
     b = b'abcdefg'

From c4f5081bf202977e37e9717f3d9e77ff759d5ee7 Mon Sep 17 00:00:00 2001
From: Ethan Sarp <11684270+esarp@users.noreply.github.com>
Date: Fri, 9 Jan 2026 13:24:05 -0600
Subject: [PATCH 2/3] Remove PY_IDENTIFIER

---
 mypyc/lib-rt/bytes_ops.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/mypyc/lib-rt/bytes_ops.c b/mypyc/lib-rt/bytes_ops.c
index 9552e54ff5ce..ba5b64df94b3 100644
--- a/mypyc/lib-rt/bytes_ops.c
+++ b/mypyc/lib-rt/bytes_ops.c
@@ -205,12 +205,7 @@ int CPyBytes_Endswith(PyObject *self, PyObject *subobj) {
 
         return memcmp(self_buf + (self_len - subobj_len), subobj_buf, (size_t)subobj_len) == 0 ? 1 : 0;
     }
-    _Py_IDENTIFIER(endswith);
-    PyObject *name = _PyUnicode_FromId(&PyId_endswith);
-    if (name == NULL) {
-        return 2;
-    }
-    PyObject *result = PyObject_CallMethodOneArg(self, name, subobj);
+    PyObject *result = PyObject_CallMethodOneArg(self, mypyc_interned_str.endswith, subobj);
     if (result == NULL) {
         return 2;
     }

From 4c55a577587a5e6b9effd7cdd0e0685855d3f9ce Mon Sep 17 00:00:00 2001
From: Ethan Sarp <11684270+esarp@users.noreply.github.com>
Date: Fri, 9 Jan 2026 13:39:04 -0600
Subject: [PATCH 3/3] Add static data for endswith; fix test typing

---
 mypyc/lib-rt/static_data.c     | 1 +
 mypyc/lib-rt/static_data.h     | 1 +
 mypyc/test-data/run-bytes.test | 6 +++---
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/mypyc/lib-rt/static_data.c b/mypyc/lib-rt/static_data.c
index c119bec56467..f723223823bf 100644
--- a/mypyc/lib-rt/static_data.c
+++ b/mypyc/lib-rt/static_data.c
@@ -46,6 +46,7 @@ intern_strings(void) {
     INTERN_STRING(clear, "clear");
     INTERN_STRING(close_, "close");
     INTERN_STRING(copy, "copy");
+    INTERN_STRING(endswith, "endswith");
     INTERN_STRING(keys, "keys");
     INTERN_STRING(items, "items");
     INTERN_STRING(join, "join");
diff --git a/mypyc/lib-rt/static_data.h b/mypyc/lib-rt/static_data.h
index f779504b6c20..efc2e7fd2e78 100644
--- a/mypyc/lib-rt/static_data.h
+++ b/mypyc/lib-rt/static_data.h
@@ -38,6 +38,7 @@ typedef struct mypyc_interned_str_struct {
     PyObject *clear;
     PyObject *close_;
     PyObject *copy;
+    PyObject *endswith;
     PyObject *keys;
     PyObject *items;
     PyObject *join;
diff --git a/mypyc/test-data/run-bytes.test b/mypyc/test-data/run-bytes.test
index afb863a3b350..f40321a85ae2 100644
--- a/mypyc/test-data/run-bytes.test
+++ b/mypyc/test-data/run-bytes.test
@@ -238,9 +238,9 @@ def test_endswith() -> None:
     assert test.endswith(bytearray(b'string'))
     assert not test.endswith(bytearray(b'other'))
 
-    test = bytearray(b'some string')
-    assert test.endswith(b'string')
-    assert not test.endswith(b'other')
+    test2 = bytearray(b'some string')
+    assert test2.endswith(b'string')
+    assert not test2.endswith(b'other')
 
 [case testBytesSlicing]
 def test_bytes_slicing() -> None: