Be more explicit on how we handle osx clipboard.

The return values can only be bytes as we do bytes manipulations before.
So if we need to return text; we always need to decode.

We can now also leave the default encoding out; as py3compat.decode
takecare of that for us

IPython/lib/clipboard.py

@@ -1,69 +1,69 b''
 """ Utilities for accessing the platform's clipboard.
 """
 
 import subprocess
 
 from IPython.core.error import TryNext
 import IPython.utils.py3compat as py3compat
 
 class ClipboardEmpty(ValueError):
     pass
 
 def win32_clipboard_get():
     """ Get the current clipboard's text on Windows.
 
     Requires Mark Hammond's pywin32 extensions.
     """
     try:
         import win32clipboard
     except ImportError:
         raise TryNext("Getting text from the clipboard requires the pywin32 "
                       "extensions: http://sourceforge.net/projects/pywin32/")
     win32clipboard.OpenClipboard()
     try:
         text = win32clipboard.GetClipboardData(win32clipboard.CF_UNICODETEXT)
     except (TypeError, win32clipboard.error):
         try:
             text = win32clipboard.GetClipboardData(win32clipboard.CF_TEXT)
             text = py3compat.cast_unicode(text, py3compat.DEFAULT_ENCODING)
         except (TypeError, win32clipboard.error):
             raise ClipboardEmpty
     finally:
         win32clipboard.CloseClipboard()
     return text
 
-def osx_clipboard_get():
+def osx_clipboard_get() -> str:
     """ Get the clipboard's text on OS X.
     """
     p = subprocess.Popen(['pbpaste', '-Prefer', 'ascii'],
         stdout=subprocess.PIPE)
-    text, stderr = p.communicate()
+    bytes_, stderr = p.communicate()
     # Text comes in with old Mac \r line endings. Change them to \n.
-    text = text.replace(b'\r', b'\n')
-    text = py3compat.cast_unicode(text, py3compat.DEFAULT_ENCODING)
+    bytes_ = bytes_.replace(b'\r', b'\n')
+    text = py3compat.decode(bytes_)
     return text
 
 def tkinter_clipboard_get():
     """ Get the clipboard's text using Tkinter.
 
     This is the default on systems that are not Windows or OS X. It may
     interfere with other UI toolkits and should be replaced with an
     implementation that uses that toolkit.
     """
     try:
         from tkinter import Tk, TclError 
     except ImportError:
         raise TryNext("Getting text from the clipboard on this platform requires tkinter.")
         
     root = Tk()
     root.withdraw()
     try:
         text = root.clipboard_get()
     except TclError:
         raise ClipboardEmpty
     finally:
         root.destroy()
     text = py3compat.cast_unicode(text, py3compat.DEFAULT_ENCODING)
     return text