Fix exception causes all over the codebase

Author: cool-RR

prompt_toolkit/input/vt100.py

@@ -48,13 +48,13 @@ def __init__(self, stdin: TextIO) -> None:
         try:
             # This should not raise, but can return 0.
             stdin.fileno()
-        except io.UnsupportedOperation:
+        except io.UnsupportedOperation as e:
             if "idlelib.run" in sys.modules:
                 raise io.UnsupportedOperation(
                     "Stdin is not a terminal. Running from Idle is not supported."
-                )
+                ) from e
             else:
-                raise io.UnsupportedOperation("Stdin is not a terminal.")
+                raise io.UnsupportedOperation("Stdin is not a terminal.") from e
 
         # Even when we have a file descriptor, it doesn't mean it's a TTY.
         # Normally, this requires a real TTY device, but people instantiate

prompt_toolkit/key_binding/bindings/named_commands.py

@@ -55,8 +55,8 @@ def get_by_name(name: str) -> Binding:
     """
     try:
         return _readline_commands[name]
-    except KeyError:
-        raise KeyError("Unknown Readline command: %r" % name)
+    except KeyError as e:
+        raise KeyError("Unknown Readline command: %r" % name) from e
 
 
 #

prompt_toolkit/layout/layout.py

@@ -59,10 +59,10 @@ def __init__(
         if focused_element is None:
             try:
                 self._stack.append(next(self.find_all_windows()))
-            except StopIteration:
+            except StopIteration as e:
                 raise InvalidLayoutError(
                     "Invalid layout. The layout does not contain any Window object."
-                )
+                ) from e
         else:
             self.focus(focused_element)