IDLE: ScrolledCanvas.zoom_height calls idlelib.zoomheight.zoom_height, which has not existed since 2019

[tony-CloseAI]

Bug report

idlelib.tree.ScrolledCanvas.zoom_height calls a module-level function that has not existed since 2019, so the binding raises as soon as it fires.

Where: Lib/idlelib/tree.py, ScrolledCanvas.zoom_height (line 459 on main), bound to <Alt-2> on the canvas:

def zoom_height(self, event):
    zoomheight.zoom_height(self.master)

idlelib/zoomheight.py has had no module-level zoom_height since the Zoom Height rework (gh-81220, PRs #13576 and #13678, 2019): zooming is now ZoomHeight(editwin).zoom_height(), which only reads editwin.top.

Reproduce (3.13.5, but the call is the same on main):

>>> from idlelib import zoomheight
>>> zoomheight.zoom_height
AttributeError: module 'idlelib.zoomheight' has no attribute 'zoom_height'. Did you mean: 'ZoomHeight'?

Pressing Alt-2 in a tree window (Path Browser, Module Browser, the debugger's stack viewer) raises the same AttributeError out of the Tk callback.

Proposed fix — ZoomHeight needs only the toplevel window of what it zooms:

+from types import SimpleNamespace
+
 from idlelib import zoomheight
@@
     def zoom_height(self, event):
-        zoomheight.zoom_height(self.master)
+        # ZoomHeight needs only the toplevel window of what it zooms.
+        top = self.canvas.winfo_toplevel()
+        zoomheight.ZoomHeight(SimpleNamespace(top=top)).zoom_height()
         return "break"

Checked by calling ScrolledCanvas.zoom_height from main's sources against a stand-in toplevel: the current code raises AttributeError; the fixed code maximizes the window height (400x300+10+20 -> 400x760+10+0).

If a SimpleNamespace stand-in is not wanted here, ZoomHeight.zoom_height could instead take the toplevel directly; happy to send a PR either way.

Environment: Windows 11, CPython 3.13.5; the line is unchanged on main.

---

Found while auditing installed code with a verification tool I am building; the reproduction above was run on the version named, and the proposed fix was applied to a local copy and run as well. Report drafted with AI assistance.

Linked PRs

• gh-157762: Fix Alt-2 zoom height binding in IDLE tree windows #157772

[serhiy-storchaka]

ScrolledCanvas and this binding are removed in #157029, which converts the browsers and the stack viewer to ttk.Treeview.

[terryjreedy]

Tony, the issue message is nicely written. However, after thinking about it, I am putting this on hold pending resolution of the replacement issue and a decision whether to make the new versions zoomable.

When I revised zoomheight, I did not know that it worked on scrolled canvases. The detailed user interaction for its instances is not documented. I hope to do better with the replacements.

[tony-CloseAI]

Thanks, both - happy to leave this on hold, and #157029 clearly supersedes it.

One measurement for the "detailed user interaction is not documented" part, in case it helps the decision about whether the replacements should be zoomable. Calling ScrolledCanvas.zoom_height with the replacement call -ZoomHeight(SimpleNamespace(top=self.canvas.winfo_toplevel())).zoom_height() - against a stand-in toplevel holding a canvas, on a 1536x864 screen with 3.13.5:

before        400x300+10+20
first call    400x785+10+0
second call   404x304+10+0

So the binding toggled the height of the whole browser window and left the width and x alone; in my stand-in the restore came back 4px larger in each direction and did not put y back. ZoomHeight.__init__ reads nothing but editwin.top, so no other part of the canvas or the browser was involved.

I have not run a pre-2019 build, so that is what the replacement does, not a reproduction of the original behaviour.