Issue #15318: Prevent writing to sys.stdin.

Patch by Roger Serwy and myself.

Lib/idlelib/PyShell.py

@@ -11,6 +11,7 @@ import time
 import threading
 import traceback
 import types
+import io
 
 import linecache
 from code import InteractiveInterpreter
@@ -422,6 +423,9 @@ class ModifiedInterpreter(InteractiveInterpreter):
         except socket.timeout, err:
             self.display_no_subprocess_error()
             return None
+        # Can't regiter self.tkconsole.stdin, since run.py wants to
+        # call non-TextIO methods on it (such as getvar)
+        # XXX should be renamed to "console"
         self.rpcclt.register("stdin", self.tkconsole)
         self.rpcclt.register("stdout", self.tkconsole.stdout)
         self.rpcclt.register("stderr", self.tkconsole.stderr)
@@ -875,13 +879,14 @@ class PyShell(OutputWindow):
         self.save_stderr = sys.stderr
         self.save_stdin = sys.stdin
         from idlelib import IOBinding
+        self.stdin = PseudoInputFile(self)
         self.stdout = PseudoFile(self, "stdout", IOBinding.encoding)
         self.stderr = PseudoFile(self, "stderr", IOBinding.encoding)
         self.console = PseudoFile(self, "console", IOBinding.encoding)
         if not use_subprocess:
             sys.stdout = self.stdout
             sys.stderr = self.stderr
-            sys.stdin = self
+            sys.stdin = self.stdin
         #
         self.history = self.History(self.text)
         #
@@ -1279,6 +1284,15 @@ class PseudoFile(object):
     def isatty(self):
         return True
 
+class PseudoInputFile(object):
+    def __init__(self, shell):
+        self.readline = shell.readline
+        self.isatty = shell.isatty
+
+    def write(self, s):
+        raise io.UnsupportedOperation("not writable")
+    writelines = write
+
 
 usage_msg = """\