text_editor.py

import tkinter as tk
from tkinter.filedialog import askopenfilename, asksaveasfilename

window = tk.Tk()
window.title("SI Code")
window.columnconfigure(0, weight=0, minsize=250)
window.columnconfigure(1, weight=1, minsize=400)
window.rowconfigure(0, weight=1, minsize=600)

# event handlers


def open_file():
    filepath = askopenfilename(
        filetypes=[("Text Files", "*.txt"), ("All Files", "*.*")]
    )
    if not filepath:
        return
    txt_edit.delete("1.0", tk.END)
    with open(filepath, "r") as input_file:
        text = input_file.read()
        txt_edit.insert(tk.END, text)
    window.title(f"SI Code - {filepath}")


def save_file():
    filepath = asksaveasfilename(
        defaultextension="txt",
        filetypes=[("Text Files", "*.txt"), ("All Files", "*.*")],
    )
    if not filepath:
        return
    with open(filepath, "w") as output_file:
        text = txt_edit.get("1.0", tk.END)
        output_file.write(text)
    window.title(f"SI Code - {filepath}")


# frames
left__Frame = tk.Frame(master=window, bg="white", width=200, padx=10, pady=15)

# components
txt_edit = tk.Text(window, bg="#eaeaea", fg="#222",
                   borderwidth=0, relief=tk.FLAT, padx=10, pady=10)
btn_open = tk.Button(left__Frame, text="Open",
                     padx=5, pady=5, width=31, relief=tk.FLAT, bg="#eaeaea", command=open_file)
btn_save = tk.Button(left__Frame, text="Save As...",
                     padx=5, pady=5, width=31, relief=tk.FLAT, bg="#eaeaea", command=save_file)

# packing everything up
txt_edit.grid(row=0, column=1, sticky="nesw")
left__Frame.grid(row=0, column=0,  sticky="nesw")
btn_open.grid(row=0, column=0, sticky="nesw")
btn_save.grid(row=1, column=0, sticky="nesw")
window.mainloop()