Lambda function in for loop to bind keywords in tkinter

Question

I am very new to Python an tkinter. I am developing a keyboard using tkinter. I have created a text box and I am trying to bind keys to it so that users can use keyboard for input. I want to print different keys when a key is pressed. For an example, I want to print P when 'p' is pressed, A when 'a' is pressed. I know I can manually type in each key and add a function to print the required value but that would be time consuming so I decided to use a dictionary.

Below is the code for this.

def print_letter(letter):
    if letter == "backspace":
        text.configure(state="normal")
        value = text.get("1.0", "end")
        text.delete("1.0", "end")
        text.insert("1.0", value[:-2])
        text.configure(state="disabled")
    else:        
        text.configure(state="normal")
        text.insert("end", letter)
        text.configure(state="disabled")

    letters = {
        'a': 'A',
        'b': 'B',
        'c': 'C',
        'd': 'D',
        'e': 'E',
    }

    root = tk.Tk()
    root.geometry("800x415")
    root.resizable(False, False)

    text = tk.Text(text_frame, width=97, height=15)
    text.configure(state="disabled")
    text.grid(row=0, column=0, sticky="EW")
    text.focus_set()

    for key, value in letters.items():
        text.bind(key, lambda value: print_letter(letters.get(key)))

But only the last value in the dictionary is bounded to any key I press. I saw a few posts on SO and they all suggested the below options:

text.bind(key, lambda value=value: print_letter(letters.get(key)))
text.bind(key, lambda args=value: print_letter(letters.get(key)))

All the above gave me the same result.

Any help is appreciated.

Does this answer your question? tkinter creating buttons in for loop passing command arguments — Karl Knechtel
– Karl Knechtel, Commented Aug 14, 2022 at 20:57

Axe319 · Accepted Answer · 2020-05-11 17:08:57Z

1

My personal preference is to use functools.partial rather than lambda since it freezes the arguments. Here is an example of it in practice.

import tkinter as tk
from functools import partial

# here we add an *args argument 
# since tkinter will also send the keystroke
# as an argument
def print_letter(letter, *args):
    if letter == "backspace":
        text.configure(state="normal")
        value = text.get("1.0", "end")
        text.delete("1.0", "end")
        text.insert("1.0", value[:-2])
        text.configure(state="disabled")
    else:      
        text.configure(state="normal")
        text.insert("end", letter)
        text.configure(state="disabled")

letters = {
    'a': 'A',
    'b': 'B',
    'c': 'C',
    'd': 'D',
    'e': 'E',
}
root = tk.Tk()
root.geometry("800x415")
root.resizable(False, False)
text = tk.Text(root, width=97, height=15)
text.configure(state="disabled")
text.grid(row=0, column=0, sticky="EW")
text.focus_set()
for key, value in letters.items():
    # partial takes unlimited args.
    # The first being the function name 
    # and subsequent ones being the arguments
    text.bind(key, partial(print_letter, value))

root.mainloop()

answered May 11, 2020 at 17:08

Axe319

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1 Comment

Arun Over a year ago

That worked! Thank you very much. I saw many posts where the community is divided between using lamda and functools.partial. Thanks again.

rizerphe · Accepted Answer · 2020-05-11 16:34:26Z

0

If I've understood your question correctly, you need sth. like this:

l = []

for _ in range(10):
    l.append(lambda v=_: print(v))

Hope that's helpful!

answered May 11, 2020 at 16:34

rizerphe

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2 Comments

Arun Over a year ago

Thanks for the comment. So this would create a list with lambda functions. How would I bind keys to individual lambda functions in the list?

rizerphe Over a year ago

for key, value in letters.items(): text.bind(key, lambda value=key: print_letter(letters.get(value)))

Thomas · Accepted Answer · 2022-08-18 11:19:14Z

0

It should work:

l = []

for _ in range(10):
    l.append(lambda v=_: print(v))

edited Aug 18, 2022 at 11:19

Thomas

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answered Aug 14, 2022 at 21:03

salihbugra

1

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