Issue #12591: Allow io.TextIOWrapper to work with raw IO objects (without

a read1() method), and add an undocumented *write_through* parameter to
mandate unbuffered writes.

2 files changed, 27 insertions, 2 deletions

diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index b79d5fc6c1..78c6d95c23 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -1472,7 +1472,7 @@ class TextIOWrapper(TextIOBase):
     _CHUNK_SIZE = 2048
 
     def __init__(self, buffer, encoding=None, errors=None, newline=None,
-                 line_buffering=False):
+                 line_buffering=False, write_through=False):
         if newline is not None and not isinstance(newline, str):
             raise TypeError("illegal newline type: %r" % (type(newline),))
         if newline not in (None, "", "\n", "\r", "\r\n"):
@@ -1515,6 +1515,7 @@ class TextIOWrapper(TextIOBase):
         self._decoded_chars_used = 0  # offset into _decoded_chars for read()
         self._snapshot = None  # info for reconstructing decoder state
         self._seekable = self._telling = self.buffer.seekable()
+        self._has_read1 = hasattr(self.buffer, 'read1')
 
         if self._seekable and self.writable():
             position = self.buffer.tell()
@@ -1680,7 +1681,10 @@ class TextIOWrapper(TextIOBase):
             # len(dec_buffer) bytes ago with decoder state (b'', dec_flags).
 
         # Read a chunk, decode it, and put the result in self._decoded_chars.
-        input_chunk = self.buffer.read1(self._CHUNK_SIZE)
+        if self._has_read1:
+            input_chunk = self.buffer.read1(self._CHUNK_SIZE)
+        else:
+            input_chunk = self.buffer.read(self._CHUNK_SIZE)
         eof = not input_chunk
         self._set_decoded_chars(self._decoder.decode(input_chunk, eof))
 
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 39fda2beea..0ca621c39d 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -2307,6 +2307,27 @@ class TextIOWrapperTest(unittest.TestCase):
         with self.assertRaises(AttributeError):
             txt.buffer = buf
 
+    def test_rawio(self):
+        # Issue #12591: TextIOWrapper must work with raw I/O objects, so
+        # that subprocess.Popen() can have the required unbuffered
+        # semantics with universal_newlines=True.
+        raw = self.MockRawIO([b'abc', b'def', b'ghi\njkl\nopq\n'])
+        txt = self.TextIOWrapper(raw, encoding='ascii', newline='\n')
+        # Reads
+        self.assertEqual(txt.read(4), 'abcd')
+        self.assertEqual(txt.readline(), 'efghi\n')
+        self.assertEqual(list(txt), ['jkl\n', 'opq\n'])
+
+    def test_rawio_write_through(self):
+        # Issue #12591: with write_through=True, writes don't need a flush
+        raw = self.MockRawIO([b'abc', b'def', b'ghi\njkl\nopq\n'])
+        txt = self.TextIOWrapper(raw, encoding='ascii', newline='\n',
+                                 write_through=True)
+        txt.write('1')
+        txt.write('23\n4')
+        txt.write('5')
+        self.assertEqual(b''.join(raw._write_stack), b'123\n45')
+
 class CTextIOWrapperTest(TextIOWrapperTest):
 
     def test_initialization(self):