python · serhiy-storchaka · Jun 6, 2026 · Dec 12, 2019 · Dec 27, 2023 · Dec 27, 2023
@@ -61,6 +61,7 @@ def set_filename_change_hook(self, hook):
        self.filename_change_hook = hook

    filename = None
+    file_timestamp = None
    dirname = None

    def set_filename(self, filename):
@@ -127,6 +128,7 @@ def loadfile(self, filename):
                    chars = f.read()
                    fileencoding = f.encoding
                    eol_convention = f.newlines
+                    file_timestamp = self.getmtime(filename)
                    converted = False
            except (UnicodeDecodeError, SyntaxError):
                # Wait for the editor window to appear
@@ -142,6 +144,7 @@ def loadfile(self, filename):
                    chars = f.read()
                    fileencoding = f.encoding
                    eol_convention = f.newlines
+                    file_timestamp = self.getmtime(filename)
                    converted = True
        except OSError as err:
            messagebox.showerror("I/O Error", str(err), parent=self.text)
@@ -170,6 +173,7 @@ def loadfile(self, filename):
        self.text.insert("1.0", chars)
        self.reset_undo()
        self.set_filename(filename)
+        self.file_timestamp = file_timestamp
        if converted:
            # We need to save the conversion results first
            # before being able to execute the code
@@ -206,7 +210,26 @@ def save(self, event):
        if not self.filename:
            self.save_as(event)
        else:
+            # Check the time of most recent content modification so the
+            # user doesn't accidentally overwrite a newer version of the file.
+            try:
+                file_timestamp = self.getmtime(self.filename)
+            except OSError:
+                pass
+            else:
+                if self.file_timestamp != file_timestamp:
+                    confirm = messagebox.askokcancel(
+                        title="File has changed",
+                        message=(
+                            "The file has changed on disk since reading it!\n\n"
+                            "Do you really want to overwrite it?"),
+                        default=messagebox.CANCEL,
+                        parent=self.text)
+                    if not confirm:
+                        return "break"
+
            if self.writefile(self.filename):
+                self.file_timestamp = self.getmtime(self.filename)
                self.set_saved(True)
                try:
                    self.editwin.store_file_breaks()
@@ -219,6 +242,7 @@ def save_as(self, event):
        filename = self.asksavefile()
        if filename:
            if self.writefile(filename):
+                self.file_timestamp = self.getmtime(filename)
                self.set_filename(filename)
                self.set_saved(1)
                try:
@@ -251,6 +275,9 @@ def writefile(self, filename):
                                   parent=self.text)
            return False

+    def getmtime(self, filename):
+        return os.stat(filename).st_mtime
+
    def fixnewlines(self):
        """Return text with os eols.


diff --git a/Misc/NEWS.d/next/IDLE/2019-12-12-03-18-02.bpo-6699.1CqJFG.rst b/Misc/NEWS.d/next/IDLE/2019-12-12-03-18-02.bpo-6699.1CqJFG.rst
@@ -0,0 +1 @@
+Warn the user if a file will be overwritten when saving.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Warn the user if a file will be overwritten when saving.