Change Clipboard.synchronized_changes() to raise an error on timeout

Re: dictation-toolbox#390.

This context manager now always raises an error on timeout.  This
makes more sense than failing silently.

Author: drmfinlay

dragonfly/windows/base_clipboard.py

@@ -163,7 +163,8 @@ def synchronized_changes(cls, timeout, step=0.001, formats=None,
         """
             Context manager for synchronizing local and system clipboard
             changes.  This takes the same arguments as the
-            :meth:`wait_for_change` method.
+            :meth:`wait_for_change` method.  A ``RuntimeError`` is raised if
+            the system clipboard does not change.
 
             Arguments:
              - *timeout* (float) -- timeout in seconds.
@@ -197,8 +198,13 @@ def synchronized_changes(cls, timeout, step=0.001, formats=None,
             # Yield for clipboard operations.
             yield
         finally:
-            # Wait for the system clipboard to change.
-            cls.wait_for_change(timeout, step, formats, initial_clipboard)
+            # Wait for the system clipboard to change, raising an error on
+            #  failure.
+            changed = cls.wait_for_change(timeout, step, formats,
+                                          initial_clipboard)
+            if not changed:
+                message = "Timed out waiting for clipboard to change"
+                raise RuntimeError(message)
 
     #-----------------------------------------------------------------------
 

dragonfly/windows/win32_clipboard.py

@@ -217,18 +217,21 @@ def wait_for_change(cls, timeout, step=0.001, formats=None,
     @classmethod
     @contextlib.contextmanager
     def synchronized_changes(cls, timeout, step=0.001, formats=None,
-                             initial_clipboard=None, raise_exception_on_timeout=False):
+                             initial_clipboard=None):
         seq_no = win32clipboard.GetClipboardSequenceNumber()
         if formats and not initial_clipboard:
             initial_clipboard = cls(from_system=True)
         try:
             # Yield for clipboard operations.
             yield
         finally:
-            # Wait for the system clipboard to change.
-            if not cls._wait_for_change(timeout, step, formats, initial_clipboard,
-                                 seq_no) and raise_exception_on_timeout:
-                raise TimeoutError("Timed out waiting for clipboard to change.")
+            # Wait for the system clipboard to change, raising an error on
+            #  failure.
+            changed = cls._wait_for_change(timeout, step, formats,
+                                           initial_clipboard, seq_no)
+            if not changed:
+                message = "Timed out waiting for clipboard to change"
+                raise RuntimeError(message)
 
     #-----------------------------------------------------------------------