Support name and mode attributes on all file types.

Don't read more than one line when reading text from a tty device.
Add peek() and read1() methods.
Return str instead of unicode when return ASCII characters in text mode.

Lib/io.py

@@ -18,6 +18,7 @@ XXX don't use assert to validate input requirements
 XXX whenever an argument is None, use the default value
 XXX read/write ops should check readable/writable
 XXX buffered readinto should work with arbitrary buffer objects
+XXX use incremental encoder for text output, at least for UTF-16
 """
 
 __author__ = ("Guido van Rossum <guido@python.org>, "
@@ -137,6 +138,8 @@ def open(file, mode="r", buffering=None, *, encoding=None, newline=None):
         raise ValueError("invalid buffering size")
     if buffering == 0:
         if binary:
+            raw._name = file
+            raw._mode = mode
             return raw
         raise ValueError("can't have unbuffered text I/O")
     if updating:
@@ -147,8 +150,13 @@ def open(file, mode="r", buffering=None, *, encoding=None, newline=None):
         assert reading
         buffer = BufferedReader(raw, buffering)
     if binary:
+        buffer.name = file
+        buffer.mode = mode
         return buffer
-    return TextIOWrapper(buffer, encoding, newline)
+    text = TextIOWrapper(buffer, encoding, newline)
+    text.name = file
+    text.mode = mode
+    return text
 
 
 class IOBase:
@@ -349,6 +357,14 @@ class FileIO(_fileio._FileIO, RawIOBase):
         _fileio._FileIO.close(self)
         RawIOBase.close(self)
 
+    @property
+    def name(self):
+        return self._name
+
+    @property
+    def mode(self):
+        return self._mode
+
 
 class SocketIO(RawIOBase):
 
@@ -628,7 +644,6 @@ class BufferedReader(_BufferedIOMixin):
             to_read = max(self.buffer_size,
                           n if n is not None else 2*len(self._read_buf))
             current = self.raw.read(to_read)
-
             if current in (b"", None):
                 nodata_val = current
                 break
@@ -642,6 +657,39 @@ class BufferedReader(_BufferedIOMixin):
             out = nodata_val
         return out
 
+    def peek(self, n=0, *, unsafe=False):
+        """Returns buffered bytes without advancing the position.
+
+        The argument indicates a desired minimal number of bytes; we
+        do at most one raw read to satisfy it.  We never return more
+        than self.buffer_size.
+
+        Unless unsafe=True is passed, we return a copy.
+        """
+        want = min(n, self.buffer_size)
+        have = len(self._read_buf)
+        if have < want:
+            to_read = self.buffer_size - have
+            current = self.raw.read(to_read)
+            if current:
+                self._read_buf += current
+        result = self._read_buf
+        if unsafe:
+            result = result[:]
+        return result
+
+    def read1(self, n):
+        """Reads up to n bytes.
+
+        Returns up to n bytes.  If at least one byte is buffered,
+        we only return buffered bytes.  Otherwise, we do one
+        raw read.
+        """
+        if n <= 0:
+            return b""
+        self.peek(1, unsafe=True)
+        return self.read(min(n, len(self._read_buf)))
+
     def tell(self):
         return self.raw.tell() - len(self._read_buf)
 
@@ -746,6 +794,12 @@ class BufferedRWPair(BufferedIOBase):
     def write(self, b):
         return self.writer.write(b)
 
+    def peek(self, n=0, *, unsafe=False):
+        return self.reader.peek(n, unsafe=unsafe)
+
+    def read1(self, n):
+        return self.reader.read1(n)
+
     def readable(self):
         return self.reader.readable()
 
@@ -799,6 +853,14 @@ class BufferedRandom(BufferedWriter, BufferedReader):
         self.flush()
         return BufferedReader.readinto(self, b)
 
+    def peek(self, n=0, *, unsafe=False):
+        self.flush()
+        return BufferedReader.peek(self, n, unsafe=unsafe)
+
+    def read1(self, n):
+        self.flush()
+        return BufferedReader.read1(self, n)
+
     def write(self, b):
         if self._read_buf:
             self.raw.seek(-len(self._read_buf), 1) # Undo readahead
@@ -932,6 +994,7 @@ class TextIOWrapper(TextIOBase):
             b = bytes(b)
         n = self.buffer.write(b)
         if "\n" in s:
+            # XXX only if isatty
             self.flush()
         self._snapshot = self._decoder = None
         return len(s)
@@ -951,11 +1014,11 @@ class TextIOWrapper(TextIOBase):
     def _read_chunk(self):
         assert self._decoder is not None
         if not self._telling:
-            readahead = self.buffer.read(self._CHUNK_SIZE)
+            readahead = self.buffer.read1(self._CHUNK_SIZE)
             pending = self._decoder.decode(readahead, not readahead)
             return readahead, pending
         decoder_state = pickle.dumps(self._decoder, 2)
-        readahead = self.buffer.read(self._CHUNK_SIZE)
+        readahead = self.buffer.read1(self._CHUNK_SIZE)
         pending = self._decoder.decode(readahead, not readahead)
         self._snapshot = (decoder_state, readahead, pending)
         return readahead, pending
@@ -1043,6 +1106,14 @@ class TextIOWrapper(TextIOBase):
         self._decoder = decoder
         return orig_pos
 
+    def _simplify(self, u):
+        # XXX Hack until str/unicode unification: return str instead
+        # of unicode if it's all ASCII
+        try:
+            return str(u)
+        except UnicodeEncodeError:
+            return u
+
     def read(self, n: int = -1):
         decoder = self._decoder or self._get_decoder()
         res = self._pending
@@ -1050,7 +1121,7 @@ class TextIOWrapper(TextIOBase):
             res += decoder.decode(self.buffer.read(), True)
             self._pending = ""
             self._snapshot = None
-            return res
+            return self._simplify(res)
         else:
             while len(res) < n:
                 readahead, pending = self._read_chunk()
@@ -1058,7 +1129,7 @@ class TextIOWrapper(TextIOBase):
                 if not readahead:
                     break
             self._pending = res[n:]
-            return res[:n]
+            return self._simplify(res[:n])
 
     def next(self) -> str:
         self._telling = False
@@ -1074,9 +1145,9 @@ class TextIOWrapper(TextIOBase):
             # XXX Hack to support limit argument, for backwards compatibility
             line = self.readline()
             if len(line) <= limit:
-                return line
+                return self._simplify(line)
             line, self._pending = line[:limit], line[limit:] + self._pending
-            return line
+            return self._simplify(line)
 
         line = self._pending
         start = 0
@@ -1129,6 +1200,6 @@ class TextIOWrapper(TextIOBase):
         # XXX Update self.newlines here if we want to support that
 
         if self._fix_newlines and ending not in ("\n", ""):
-            return line[:endpos] + "\n"
+            return self._simplify(line[:endpos] + "\n")
         else:
-            return line[:nextpos]
+            return self._simplify(line[:nextpos])