python · msullivan · Aug 5, 2021 · Aug 4, 2021
diff --git a/mypyc/lib-rt/CPy.h b/mypyc/lib-rt/CPy.h
@@ -400,6 +400,8 @@ Py_ssize_t CPyStr_Size_size_t(PyObject *str);
 // Bytes operations
 
 
+PyObject *CPyBytes_Join(PyObject *sep, PyObject *iter);
+
 
 // Set operations
 

diff --git a/mypyc/lib-rt/bytes_ops.c b/mypyc/lib-rt/bytes_ops.c
@@ -4,3 +4,13 @@
 
 #include <Python.h>
 #include "CPy.h"
+
+// Like _PyBytes_Join but fallback to dynamic call if 'sep' is not bytes
+// (mostly commonly, for bytearrays)
+PyObject *CPyBytes_Join(PyObject *sep, PyObject *iter) {
+    if (PyBytes_CheckExact(sep)) {
+        return _PyBytes_Join(sep, iter);
+    } else {
+        return PyObject_CallMethod(sep, "join", "(O)", iter);
+    }
+}
diff --git a/mypyc/primitives/bytes_ops.py b/mypyc/primitives/bytes_ops.py
@@ -5,7 +5,7 @@
     object_rprimitive, bytes_rprimitive, list_rprimitive, dict_rprimitive,
     str_rprimitive, RUnion
 )
-from mypyc.primitives.registry import load_address_op, function_op
+from mypyc.primitives.registry import load_address_op, function_op, method_op
 
 
 # Get the 'bytes' type object.
@@ -29,3 +29,12 @@
     return_type=bytes_rprimitive,
     c_function_name='PyByteArray_FromObject',
     error_kind=ERR_MAGIC)
+
+# bytes.join(obj)
+method_op(
+    name='join',
+    arg_types=[bytes_rprimitive, object_rprimitive],
+    return_type=bytes_rprimitive,
+    c_function_name='CPyBytes_Join',
+    error_kind=ERR_MAGIC
+)
diff --git a/mypyc/test-data/irbuild-bytes.test b/mypyc/test-data/irbuild-bytes.test
@@ -62,3 +62,17 @@ L0:
     c = r6
     return 1
 
+
+[case testBytesJoin]
+from typing import List
+
+def f(b: List[bytes]) -> bytes:
+    return b" ".join(b)
+[out]
+def f(b):
+    b :: list
+    r0, r1 :: bytes
+L0:
+    r0 = b' '
+    r1 = CPyBytes_Join(r0, b)
+    return r1
diff --git a/mypyc/test-data/run-bytes.test b/mypyc/test-data/run-bytes.test
@@ -97,3 +97,28 @@ def test_bytearray_passed_into_bytes() -> None:
     assert f(bytearray(3))
     brr1: Any = bytearray()
     assert f(brr1)
+
+[case testBytesJoin]
+from typing import Any
+from testutil import assertRaises
+from a import bytes_subclass
+
+def test_bytes_join() -> None:
+    assert b' '.join([b'a', b'b']) == b'a b'
+    assert b' '.join([]) == b''
+
+    x: bytes = bytearray(b' ')
+    assert x.join([b'a', b'b']) == b'a b'
+    assert type(x.join([b'a', b'b'])) == bytearray
+
+    y: bytes = bytes_subclass()
+    assert y.join([]) == b'spook'
+
+    n: Any = 5
+    with assertRaises(TypeError, "can only join an iterable"):
+        assert b' '.join(n)
+
+[file a.py]
+class bytes_subclass(bytes):
+    def join(self, iter):
+        return b'spook'
Original file line number	Diff line number	Diff line change
Expand Up		@@ -400,6 +400,8 @@ Py_ssize_t CPyStr_Size_size_t(PyObject *str);
		// Bytes operations


		PyObject CPyBytes_Join(PyObject sep, PyObject *iter);


		// Set operations

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