Added warning if title argument is unused by an ImageShow viewer

Tests/test_imageshow.py

@@ -68,6 +68,20 @@ def test_viewers():
             pass
 
 
+def test_title_warning():
+    viewer = ImageShow.WindowsViewer()
+    with pytest.warns(UserWarning):
+        viewer.get_command("test.jpg", title="test")
+
+    for viewer in [
+        ImageShow.DisplayViewer(),
+        ImageShow.GmDisplayViewer(),
+        ImageShow.EogViewer(),
+    ]:
+        with pytest.warns(UserWarning):
+            viewer.get_command_ex("test.jpg", title="test")
+
+
 def test_ipythonviewer():
     pytest.importorskip("IPython", reason="IPython not installed")
     for viewer in ImageShow._viewers:

src/PIL/ImageShow.py

@@ -16,6 +16,7 @@ import shutil
 import subprocess
 import sys
 import tempfile
+import warnings
 from shlex import quote
 
 from PIL import Image
@@ -58,6 +59,11 @@ def show(image, title=None, **options):
     return 0
 
 
+def _warn_if_unused_title(options):
+    if options.get("title") is not None:
+        warnings.warn("title argument is not supported by this viewer")
+
+
 class Viewer:
     """Base class for viewers."""
 
@@ -121,6 +127,7 @@ class WindowsViewer(Viewer):
     options = {"compress_level": 1}
 
     def get_command(self, file, **options):
+        _warn_if_unused_title(options)
         return (
             f'start "Pillow" /WAIT "{file}" '
             "&& ping -n 2 127.0.0.1 >NUL "
@@ -147,6 +154,7 @@ class MacViewer(Viewer):
 
     def show_file(self, file, **options):
         """Display given file"""
+        _warn_if_unused_title(options)
         fd, path = tempfile.mkstemp()
         with os.fdopen(fd, "w") as f:
             f.write(file)
@@ -190,6 +198,7 @@ class DisplayViewer(UnixViewer):
     """The ImageMagick ``display`` command."""
 
     def get_command_ex(self, file, **options):
+        _warn_if_unused_title(options)
         command = executable = "display"
         return command, executable
 
@@ -198,6 +207,7 @@ class GmDisplayViewer(UnixViewer):
     """The GraphicsMagick ``gm display`` command."""
 
     def get_command_ex(self, file, **options):
+        _warn_if_unused_title(options)
         executable = "gm"
         command = "gm display"
         return command, executable
@@ -207,6 +217,7 @@ class EogViewer(UnixViewer):
     """The GNOME Image Viewer ``eog`` command."""
 
     def get_command_ex(self, file, **options):
+        _warn_if_unused_title(options)
         executable = "eog"
         command = "eog -n"
         return command, executable