How to shrink a frame in tkinter after removing contents?

Question

Most of the topics I came across deals with how to not shrink the Frame with contents, but I'm interested in shrinking it back after the destruction of said contents. Here's an example:

import tkinter as tk
root = tk.Tk()
lbl1 = tk.Label(root, text='Hello!')
lbl1.pack()
frm = tk.Frame(root, bg='black')
frm.pack()
lbl3 = tk.Label(root, text='Bye!')
lbl3.pack()
lbl2 = tk.Label(frm, text='My name is Foo')
lbl2.pack()

So far I should see this in my window:

Hello!
My name is Foo
Bye!

That's great, but I want to keep the middle layer interchangeable and hidden based on needs. So if I destroy the lbl2 inside:

lbl2.destroy()

I want to see:

Hello!
Bye!

But what I see instead:

Hello!
███████
Bye!

I want to shrink frm back to basically non-existence because I want to keep the order of my main widgets intact. Ideally, I want to run frm.pack(fill=tk.BOTH, expand=True) so that my widgets inside can scale accordingly. However if this interferes with the shrinking, I can live without fill/expand.

I've tried the following:

1. pack_propagate(0): This actually doesn't expand the frame at all past pack().
2. Re-run frm.pack(): but this ruins the order of my main widgets.
3. .geometry(''): This only works on the root window - doesn't exist for Frames.
4. frm.config(height=0): Oddly, this doesn't seem to change anything at all.
5. frm.pack_forget(): From this answer, however it doesn't bring it back.

The only option it leaves me is using a grid manager, which works I suppose, but not exactly what I'm looking for... so I'm interested to know if there's another way to achieve this.

Answer 1

Question: Shrink a Frame after removing the last widget?

Bind to the <'Expose'> event and .configure(height=1) if no children.

---

Reference:

• Expose

  An Expose event is generated whenever all or part of a widget should be redrawn

---

import tkinter as tk

class App(tk.Tk):
    def __init__(self):
        super().__init__()

        tk.Label(self, text='Hello!').pack()
        self.frm = frm = tk.Frame(self, bg='black')
        frm.pack()
        tk.Label(self, text='Bye!').pack()
        tk.Label(frm, text='My name is Foo').pack()

        self.menubar = tk.Menu()
        self.config(menu=self.menubar)
        self.menubar.add_command(label='delete', command=self.do_destroy)
        self.menubar.add_command(label='add', command=self.do_add)

        frm.bind('<Expose>', self.on_expose)

    def do_add(self):
        tk.Label(self.frm, text='My name is Foo').pack()
        
    def do_destroy(self):
        w = self.frm
        if w.children:
            child = list(w.children).pop(0)
            w.children[child].destroy()

    def on_expose(self, event):
        w = event.widget
        if not w.children:
            w.configure(height=1)
        
                            
if __name__ == "__main__":
    App().mainloop()

---

Question: Re-run frm.pack(): but this ruins the order of my main widgets.
frm.pack_forget(), however it doesn't bring it back.

Pack has the options before= and after. This allows to pack a widget relative to other widgets.

---

Reference:

• -before

  Use its master as the master for the slaves, and insert the slaves just before other in the packing order.

---

Example using before= and self.lbl3 as anchor. The Frame are removed using .pack_forget() if no children and get repacked at the same place in the packing order.

Note: I show only the relevant parts!

class App(tk.Tk):
    def __init__(self):
        ...
        self.frm = frm = tk.Frame(self, bg='black')
        frm.pack()
        self.lbl3 = tk.Label(self, text='Bye!')
        self.lbl3.pack()
        ...

    def on_add(self):
        try:
            self.frm.pack_info()
        except:
            self.frm.pack(before=self.lbl3, fill=tk.BOTH, expand=True)

        tk.Label(self.frm, text='My name is Foo').pack()

    def on_expose(self, event):
        w = event.widget
        if not w.children:
            w.pack_forget()

Tested with Python: 3.5 - 'TclVersion': 8.6 'TkVersion': 8.6