We Keep Coding

How to set ‘in' attribute in ' pack' method (tkinter library)?

from tkinter import *
window=Tk()
Button(window,text='').pack(in=?)
How to set 'in' attribute in pack method? what does that mean?
I looked at the source code of the pack, but I still couldn't understand how to set the ’in' attribute about pack method.

How to set 'in' attribute in pack method?
You must use in_ rather than in. For example:
root = tk.Tk()
frame = tk.Frame(root)
button = tk.Button(root)
button.pack(in_=frame)
what does that mean?
When laying out a widget, every widget except the root window has a master -- some other widget which contains the widget and which controls how it is laid out. By default the master is the same as the parent. For example, if you do Button(window,text=''), the parent of the button is window, and thus its master will also default to window.
You can use in_ to change the master. For example, you could make a button be the child of the root window, but be laid out in some other frame. In the earlier example, the button is a child of the root window but will be a slave inside of the frame.
This is something you almost never need to do with tkinter, since it's usually preferable to have the parent and the master be the same widget.

Tk(), Toplevel() and winfo_toplevel(). Difference between them and how and when to use effectively?

I am trying to understand how a widget is being created. And I found above three functions are getting used in creating a widget, yet I couldn't come up with the difference and the advantage of one over the other. Even though, I had taken a look on this answer that still leaves me with confusion (and it hadn't said anything about winfo_toplevel too).
Here is my code.
from tkinter import *
root = Tk()
root.title("Root widget")
root.mainloop()
window = Toplevel()
window.title("Window widget")
window.mainloop()
On running above code "Root" widget is getting created. On closing "Root", two widgets are created with one titled "Window widget" and other being unwanted. On closing unwanted widget, "Window widget" is also getting destroyed.
What is actually happening here and how to overcome?
Another sample:
class ldo(Frame):
def __init__(self, master = None):
Frame.__init__(self,master)
self.grid()
self.appOutline()
def appOutline(self):
top = self.winfo_toplevel()
self.menuBar = Menu(top)
top["menu"] = self.menuBar
self.subMenu1 = Menu(self.menuBar)
self.menuBar.add_cascade(label = "File", menu = self.subMenu1)
app = ldo()
app.master.title("Sample UI")
app.mainloop()
On the other hand, this code is using winfo_toplevel() where the widget looks perfectly fine. Here, my assumption is, Frame plays a role of creating widget and winfo_toplevel() is an enhancing tool to other tkinter items. But would like to know what it does actually.
However, below snippet is not working:
winf = winfo_Toplevel()
winf.title("Winfo Widget")
winf.mainloop()
And returning such error:
winf = winfo_Toplevel()
NameError: name 'winfo_Toplevel' is not defined
What is the exact difference between Tk(), Toplevel() and winfo_Toplevel(). What and when should one be used effectively. Looking for really a better understanding.

On running above code "Root" widget is getting created. On closing "Root", two widgets are created with one titled "Window widget" and
other being unwanted. On closing unwanted widget, "Window widget" is
also getting destroyed. What is actually happening here and how to
overcome?
When you create any widget with the absence of an actual Tk() instance, a Tk() instance automatically gets created, thus resulting in an unwanted Toplevel-like widget when the second part of the first code snippet runs. Additionally, when a widget gets created with the absence of master option, it is assumed that the instance is a child of one of the Tk instances, in above case, there's only one, and that's the one that got automatically created. When a parent gets destroyed all widgets that are under it also gets destroyed, so when you close the unwanted widget that is an instance of Tk, the Toplevel instance also gets destroyed as its parent is destroyed.
On the second part, winfo_toplevel refers to the automatically created Tk instance again and creates other children with that automatically created Tk as the parent, which should be technically fine but would be harder to maintain as a code, than the standard ways of creating the same GUI I'd presume.
winf = winfo_Toplevel()
winf.title("Winfo Widget")
winf.mainloop()
In the code piece above, unless imported or otherwise defined winfo_Toplevel has no meaning, first of all, it's not as same as winfo_toplevel as python is case sensitive. Secondly, even if python wasn't case sensitive, it would still throw an error as it is a method and it lacks the first positional argument, which is the object instance to the class of which the winfo_toplevel method is also defined for.
Essentially, you're trying to use a case-insensitive spelling of a method, as if it is a class name such as Toplevel or Tk, which winfo_toplevel has almost nothing to do with.
Examine the following code:
import tkinter as tk
root = tk.Tk()
root.title("This is the actual Tk instance, root")
toplevel = tk.Toplevel(root)
toplevel.title("This is a Toplevel, whose parent is root"),
r_lbl = tk.Label(text="""This label is a children to the default master,
as it lacks the first positional argument for an explicit parent
assignment.""")
r_lbl2 = tk.Label(r_lbl.winfo_toplevel(), text="""This label checks who the
toplevel parent for r_lbl is, and then selects that parent as a parent
to itself.""")
r_lbl3 = tk.Label(root, text="""This label will appear on root, as it's
explicitly passed as the first positional argument, which is the parent,
as root.""")
t_lbl = tk.Label(toplevel, text="""This label will appear on toplevel, as it's
explicitly passed as the first positional argument, which is the parent,
as toplevel.""")
t_lbl2 = tk.Label(t_lbl.winfo_toplevel(), text="""This label checks who the
toplevel parent for t_lbl is, and then selects that parent as a parent
to itself.""")
r_lbl.pack()
r_lbl2.pack()
r_lbl3.pack()
t_lbl.pack()
t_lbl2.pack()
root.mainloop()
In conclusion, Tk, while being a Toplevel widget, is also the tcl interpreter for the entire GUI that runs in a thread. There can be more than one present, which is discouraged as usually multiple instances of it is unjustified, but there also has to be at least one instance present in order to have a GUI.
Toplevel can be considered to be the only visual part of a Tk instance, and it can be used when there is a need for multiple window-like widgets.
Finally, winfo_toplevel is merely a method returns the reference for the Toplevel-like parent that a widget is in, be the parent an instance of a Toplevel or a Tk.

How to capture events on tkinter child widgets?

In the following block, clicking on a_frame triggers the event handler on_frame_click, but clicking on a_label which is a child of a_frame does not. Is there a way to force a_frame to trap and handle events which originated on it's children (preferably with out having to add handlers to the children directly)? I am using Python 3.2.3.
import tkinter
def on_frame_click(e):
print("frame clicked")
tk = tkinter.Tk()
a_frame = tkinter.Frame(tk, bg="red", padx=20, pady=20)
a_label = tkinter.Label(a_frame, text="A Label")
a_frame.pack()
a_label.pack()
tk.protocol("WM_DELETE_WINDOW", tk.destroy)
a_frame.bind("<Button>", on_frame_click)
tk.mainloop()

Yes, you can do what you want, but it requires a bit of work. It's not that it's not supported, it's just that it's actually quite rare to need something like this so it's not the default behavior.
TL;DR - research "tkinter bind tags"
The Tkinter event model includes the notion of "bind tags". This is a list of tags associated with each widget. When an event is received on a widget, each bind tag is checked to see if it has a binding for the event. If so, the handler is called. If not, it continues on. If a handler returns "break", the chain is broken and no more tags are considered.
By default, the bind tags for a widget are the widget itself, the widget class, the tag for the toplevel window the widget is in, and finally the special tag "all". However, you can put any tags you want in there, and you can change the order.
The practical upshot of all this? You can add your own unique tag to every widget, then add a single binding to that tag that will be processed by all widgets. Here's an example, using your code as a starting point (I added a button widget, to show this isn't something special just for frames and labels):
import Tkinter as tkinter
def on_frame_click(e):
print("frame clicked")
def retag(tag, *args):
'''Add the given tag as the first bindtag for every widget passed in'''
for widget in args:
widget.bindtags((tag,) + widget.bindtags())
tk = tkinter.Tk()
a_frame = tkinter.Frame(tk, bg="red", padx=20, pady=20)
a_label = tkinter.Label(a_frame, text="A Label")
a_button = tkinter.Button(a_frame, text="click me!")
a_frame.pack()
a_label.pack()
a_button.pack()
tk.protocol("WM_DELETE_WINDOW", tk.destroy)
retag("special", a_frame, a_label, a_button)
tk.bind_class("special", "<Button>", on_frame_click)
tk.mainloop()
For more on bindtags, you might be interested in my answer to the question How to bind self events in Tkinter Text widget after it will binded by Text widget?. The answer addresses a different question than the one here, but it shows another example of using bind tags to solve real world problems.

I can't seem to find a direct method of automatically binding to child widgets (though there are methods of binding to an entire class of widgets and to all widgets in an application), but something like this would be easy enough.
def bind_tree(widget, event, callback, add=''):
"Binds an event to a widget and all its descendants."
widget.bind(event, callback, add)
for child in widget.children.values():
bind_tree(child, event, callback, replace_callback)
Just thought of this, but you could also put a transparent widget the size of a_frame on top of everything as a child of a_frame and bind the <Button> event to that, and then you could refer to a_frame as e.widget.master in the callback in order to make it reusable if necessary. That'd likely do what you want.

Based on what it says in the Levels of Binding section of this online Tkinter reference, it sounds like it's possible because you can bind a handler to three different levels.
To summarize:
Instance Level: Bind an event to a specific widget.
Class Level: Bind an event to all widgets of a specific class.
Application Level: Widget independent -- certain events always invoke a specific handler.
For the details please refer to the first link.
Hope this helps.

Depending on what you're trying to do, you could bind everything
print(a_label.bindtags()) # ('.!frame.!label', 'Label', '.', 'all')
tk.bind_class('.', "<Button>", on_frame_click)

Tkinter toplevel communication

If I have a button that executes a handler in relation to one toplevel window or root - can it modify a widget in another toplevel? What is the standard method of doing this?

I am not experienced in Tkinter, but I am sure its no different than PyQt4. Generally you want the parent child relationship. A parent widget contains children widgets and can modify them. The children should usually not know much about their parents and would communicate via signals or events.
When a handler fires, it should be free to modify the widgets it knows about. That is, if your top level window has 10 widgets, and contains the handler as a method, the method should be allowed to modify the 10 widgets through self attributes.
Something like:
class MyTopWindow:
def __init__(self):
self.widget1 = Widget
self.widget2 = Widget
self.button = Button
#self.button.clicked -> self.handler
def handler(self):
self.widget1.someAttribute = 1
button.click() # -> handler()
You make use of composition to build widgets inside of widgets. What you should avoid is a handler making some reference to a global widget that it really does not own.

Yes, a handler for a button (or any event) can modify any widget in any other toplevel. As long as that handler has a reference to the widget, the handler can modify it. There are no restrictions in that regard.

Trying to make a collapsible widget: How to hide/unhide all child widgets?

Im making a simplish widget that can act as a container for other widgets. One of the features of the widget is that you can expand/collapse it by clicking on it. My current method is basically looking up all child widgets of the layout and hiding them. I'm looking for any help on how to handle this properly - my current implementation has at least one serious caveat: that you can't add widgets while it's collapsed (they're added in an 'unhidden' state)
heres the setCollapsed method that is run when the widget is clicked
def collapsed(self):
return self._isCollapsed
def setCollapsed(self, collapseBool):
self._isCollapsed = collapseBool
if self.layout()!=None:
childWidgets = [self.layout().itemAt(i).widget() for i in range(self.layout().count())]
for w in childWidgets:
if isinstance(w,QtGui.QWidget):
w.setHidden(collapseBool)
if collapseBool:
self._cachedMargin = self.layout().margin()
self.layout().setMargin(0)
else:
self.layout().setMargin(self._cachedMargin)

Rather than hiding all child widgets individually, I would just hide a single parent item.