Index: repy/restrictions.py
===================================================================
--- repy/restrictions.py	(revision 2298)
+++ repy/restrictions.py	(working copy)
@@ -88,6 +88,7 @@
 known_calls = [ "canceltimer", "exitall", "file.close", "file.flush",
 	"file.__init__", "file.next", "file.read", "file.readline",
 	"file.readlines", "file.seek", "file.write", "file.writelines",
+        "file.truncate",
 	"listdir", "removefile", "gethostbyname_ex", "getmyip", "open",
 	"openconn", "recvmess", "sendmess", "settimer", "sleep",
 	"socket.close", "socket.recv", "socket.send", "stopcomm",
Index: repy/emulfile.py
===================================================================
--- repy/emulfile.py	(revision 2298)
+++ repy/emulfile.py	(working copy)
@@ -95,8 +95,11 @@
          The mode (see open)

    <Exceptions>
-      As with open, this may raise a number of errors
+      As with open, this may raise a number of errors. Additionally:

+      TypeError if the mode is not a string.
+      ValueError if the modestring is invalid.
+
    <Side Effects>
       Opens a file on disk, using a file descriptor.   When opened with "w"
       it will truncate the existing file.
@@ -105,12 +108,104 @@
       A file-like object
   """

-  restrictions.assertisallowed('open',filename,mode)
+  if type(mode) is not str:
+    raise TypeError("Attempted to open file with invalid mode (must be a string).")

-  return emulated_file(filename, mode)
+  # We just filter out 'b' / 't' in modestrings because emulated_file opens
+  # everything in binary mode for us.
+
+  originalmode = mode
+
+  if 'b' in mode:
+    mode = mode.replace('b','')
+
+  if 't' in mode:
+    mode = mode.replace('t','')
+
+  # Now we use our very safe, cross-platform open-like function and other
+  # file-object methods to emulate ANSI file modes.
+
+  file_object = None
+  if mode == "r":
+    file_object = safe_open(filename, "r")
+
+  elif mode == "r+":
+    file_object = safe_open(filename, "rw")
+
+  elif mode == "w" or mode == "w+":
+    file_object = safe_open(filename, "rw", create=True)
+    file_object.truncate()
+
+  elif mode == "a" or mode == "a+":
+    file_object = safe_open(filename, "rw", create=True)
+    file_object.seek(0, os.SEEK_END)
+
+
+  if file_object is None:
+    raise ValueError("Invalid mode ('%s') passed to open()." % originalmode)
+
+  return file_object
+
+
+
+
+def safe_open(filename, mode="r", create=False):
+  """
+   <Purpose>
+      Allows the user program to open a file safely.   This function is not
+      meant to resemble the builtin "open".
+
+   <Arguments>
+      filename:
+         The file that should be operated on
+      mode:
+         The mode:
+            "r":  Open the file for reading.
+            "rw": Open the file for reading and writing.
+
+            These are the only valid modes accepted by this version of
+            open(). Note: files opened with this function are always opened in
+            "binary" mode.
+      create:
+         If True, create the file if it doesn't exist already.
+
+   <Exceptions>
+      As with open, this may raise a number of errors. Additionally:
+
+      ValueError is raised if this is passed an invalid mode.
+
+   <Side Effects>
+      Opens a file on disk, using a file descriptor.
+
+   <Returns>
+      A file-like object
+  """
+
+  # Only allow 'r' and 'rw'.
+
+  actual_mode = None
+  if mode == "r":
+    actual_mode = "rb"
+  elif mode == "rw":
+    actual_mode = "r+b"
+
+  if actual_mode is None:
+    raise ValueError("Valid modes for opening a file in repy are 'r' and 'rw'.")

+  restrictions.assertisallowed('open', filename, actual_mode)

+  if create and not os.path.exists(filename):
+    # Create a file by opening it in write mode and then closing it.
+    restrictions.assertisallowed('open', filename, "wb")

+    create_file = emulated_file(filename, "wb")
+    create_file.close()
+
+  return emulated_file(filename, actual_mode)
+
+
+
+
 # This keeps the state for the files (the actual objects, etc.)
 fileinfo = {}

@@ -318,5 +413,16 @@
     return retval


+  def truncate(self, size=None):
+    # Truncate a file to wherever. Needed to emulate "w" / "w+" C89 file modes.
+    myfilehandle = self.filehandle
+    restrictions.assertisallowed('file.truncate', size)
+
+    if size is None:
+      return fileinfo[myfilehandle]['fobj'].truncate()
+    else:
+      return fileinfo[myfilehandle]['fobj'].truncate(size)
+
+
 # End of emulated_file class