Trac #27275: py3: fix sage.libs.readline.pyx for python3

fix doctests failures : sage -t --long src/sage/libs/readline.pyx # 10
doctests failed

URL: https://trac.sagemath.org/27275
Reported by: vklein
Ticket author(s): Vincent Klein
Reviewer(s): Erik Bray, Frédéric Chapoton

src/sage/libs/readline.pyx

@@ -10,28 +10,29 @@ EXAMPLES::
     sage: from sage.libs.readline import *
     sage: replace_line('foobar', 0)
     sage: set_point(3)
-    sage: print('current line: ' + repr(copy_text(0, get_end())))
+    sage: print('current line:', repr(copy_text(0, get_end())))
     current line: 'foobar'
-    sage: print('cursor position: {}'.format(get_point()))
+    sage: print('cursor position:', get_point())
     cursor position: 3
 
 When printing with :class:`interleaved_output` the prompt and current
 line is removed::
 
     sage: with interleaved_output():
     ....:     print('output')
-    ....:     print('current line: ' + repr(copy_text(0, get_end())))
-    ....:     print('cursor position: {}'.format(get_point()))
+    ....:     print('current line: ',
+    ....:            repr(copy_text(0, get_end())))
+    ....:     print('cursor position:', get_point())
     output
     current line: ''
     cursor position: 0
 
 After the interleaved output, the line and cursor is restored to the
 old value::
 
-    sage: print('current line: ' + repr(copy_text(0, get_end())))
+    sage: print('current line:', repr(copy_text(0, get_end())))
     current line: 'foobar'
-    sage: print('cursor position: {}'.format(get_point()))
+    sage: print('cursor position:', get_point())
     cursor position: 3
 
 Finally, clear the current line for the remaining doctests::
@@ -49,6 +50,7 @@ Finally, clear the current line for the remaining doctests::
 #                  http://www.gnu.org/licenses/
 #*****************************************************************************
 from __future__ import print_function
+from sage.cpython.string cimport str_to_bytes, bytes_to_str
 
 
 cdef extern from 'readline/readline.h':
@@ -206,7 +208,7 @@ def copy_text(pos_start, pos_end):
         sage: copy_text(1, 5)
         'ooba'
     """
-    return rl_copy_text(pos_start, pos_end)
+    return bytes_to_str(rl_copy_text(pos_start, pos_end))
 
 def replace_line(text, clear_undo):
     """
@@ -228,7 +230,7 @@ def replace_line(text, clear_undo):
         sage: copy_text(1, 5)
         'ooba'
     """
-    rl_replace_line(text, clear_undo)
+    rl_replace_line(str_to_bytes(text), clear_undo)
 
 def initialize():
     """