from __future__ import annotations
from tkinter import Event, Label
from tkinter import Tk, Text
root = Tk()
text = Text(root)
text.pack(fill="both", expand=True)
# Insert text with hidden characters
text.insert("1.0", "Hello\u00a0 World")
class Marker(Label):
    """A marker for a hidden character"""
    def __init__(self, master: Text) -> None:
        # Make the label
        self.text = master
        super().__init__(master)
    def __repr__(self) -> str:
        return f"Marker-{self._w}"
class Extension:
    """Hidden character finder"""
    def __init__(self, master: Tk) -> None:
        # Set master and mainapp
        self.master = master
        # Set other variables
        self.locations_and_markers: dict[str, Marker] = {}
        # Make binds
        self.master.bind("<Configure>", self.find_and_mark)
    def find_and_mark(self, _: Event | None = None) -> None:
        """Finds all hidden characters and marks them"""
        del _
        # Get the text widget
        # Find all hidden characters
        hidden_char_indexes: list[str] = [text.search(
            "\u00a0", "1.0", "end", regexp=True, nocase=True
        )]
        # Remove all markers
        for marker in self.locations_and_markers.values():
            marker.destroy()
        self.locations_and_markers = {}
        if hidden_char_indexes == [""]:
            return
        # Add markers
        for index in hidden_char_indexes:
            # Create the marker
            self.locations_and_markers[index] = Marker(text)
            # Get the coordinates of the character
            bbox = text.bbox(index)
            # Check that the bbox is not None
            if bbox is None:
                continue
            # Check that the character is visible and in view
            start: str = text.index("@0,0")
            end: str = text.index(f"@{text.winfo_width()},{text.winfo_height()}")
            in_view: bool = text.compare(start, "<=", index) and text.compare(
                index, "<=", end
            )
            if not in_view:
                continue
            # Get the coordinates of the character
            x: int = bbox[0]
            y: int = bbox[1]
            # Place the marker
            self.locations_and_markers[index].place(x=x, y=y, anchor="nw")
Extension(root)
root.mainloop()

...
def find_and_mark(self, e: Event) -> None:
if e.widget != self.master:
return
...