Up and down arrow inserting unwanted character in tkinter.Entry widget - python-3.x

Question

The following code produces an app with a single Entry widget. When run on MacOS using Python 3.7.3 from Homebrew, pressing the up or down arrow while inside the entry box causes a character 0xF701 to be inserted:
import tkinter as tk
root = tk.Tk()
app = tk.Frame(master=root)
app.pack()
entry = tk.Entry(app)
entry.pack()
app.mainloop()
This doesn't happen with Anaconda Python and I haven't been able to find anyone else having this issue.
By binding print to the up and down events I've been able to see that the character associated with these events is indeed 0xF700 and 0xF701.
entry.bind('<Down>', print)
entry.bind('<Up>', print)
Output after pressing up and down:
<KeyPress event state=Mod3|Mod4 keysym=Up keycode=8320768 char='\uf700' delta=8320768 x=-5 y=-50>
<KeyPress event state=Mod3|Mod4 keysym=Down keycode=8255233 char='\uf701' delta=8255233 x=-5 y=-50>
With the Anaconda Python version the output is slightly different:
<KeyPress event state=Mod3|Mod4 keysym=Up keycode=8320768 char='\uf700' x=-5 y=-50>
<KeyPress event state=Mod3|Mod4 keysym=Down keycode=8255233 char='\uf701' x=-5 y=-50>
Does anyone know of a simple solution to this problem?

Answer 1

Can validating the Entry help? The code below validates that the resulting string in Entry only contains characters in valid_chars. A more complex validation rule could be written if required.
import tkinter as tk
import re
valid_chars = re.compile(r'^[0-9A-Za-z ]*$') # Accept Alphanumeric and Space
class ValidateEntry(tk.Entry):
def __init__(self, parent, regex):
self.valid = regex
validate_cmd = (parent.register(self.validate),'%P') # %P pass the new string to validate
super().__init__( parent, validate = 'key', validatecommand = validate_cmd)
# validate = 'key' runs the validation at each keystroke.
def validate(self, new_str):
if self.valid.match(new_str): return True
return False
def do_key(ev):
print(ev.widget, ev, entry.get())
root= tk.Tk()
root.title("Validation")
fram = tk.Frame(root)
fram.grid()
entry = ValidateEntry(fram, valid_chars)
entry.grid()
entry.bind('<Down>', do_key)
entry.bind('<Up>', do_key)
root.mainloop()
This may be overkill but should work across all the platforms.

Answer 2

The release why you are getting those unknown characters in an Entry widget is because for some reason char codes of "Up" (\uf700) and "Down" (\uf701) arrows prints  when run from homebrew python but not with anaconda python not sure why is that.
You can try and see yourself by running this code with either of them.
root = Tk()
E = Entry(root)
E.bind('<Key>', lambda e: print(e.char))
E.pack()
root.mainloop()
The solution I come up with is to overwrite the main <Key> bind of Entry widget to ignore "Up" and "Down" arrows.
import tkinter as tk
class Entry(tk.Entry):
def __init__(self, master=None, cnf={}, **kw):
super(Entry, self).__init__(master=master, cnf=cnf, **kw)
self.bind_class('Entry', '<Key>', self.add_char)
def add_char(self, evt):
if evt.char != '\uf701' and evt.char != '\uf700':
self.insert('insert', evt.char)
self.xview_moveto(1)
if __name__ == "__main__":
root = tk.Tk()
E = Entry(root)
E.pack()
root.mainloop()