Tkinter ToDo: editing, colors, and task sorting

Extending a Tkinter ToDo App: Editing, Colors, Sorting, and Dates

Extending the functionality requires updating the task structure. Each task now includes fields: id, text, completed, created_at (ISO string), and priority (high/medium/low). For backward compatibility, migration of old data with default values is implemented.

Loading and saving functions ensure seamless integration:

import json
import os
from datetime import datetime

TASKS_FILE = "tasks.json"

def load_tasks():
    """Loads tasks from a JSON file with backward compatibility"""
    if not os.path.exists(TASKS_FILE):
        return []
    with open(TASKS_FILE, "r", encoding="utf-8") as f:
        try:
            tasks = json.load(f)
            # Migrate old tasks (add created_at and priority if missing)
            for task in tasks:
                if "created_at" not in task:
                    task["created_at"] = datetime.now().isoformat()
                if "priority" not in task:
                    task["priority"] = "medium"
            return tasks
        except json.JSONDecodeError:
            return []

def save_tasks(tasks):
    """Saves tasks to a JSON file"""
    with open(TASKS_FILE, "w", encoding="utf-8") as f:
        json.dump(tasks, f, ensure_ascii=False, indent=2)

def get_next_id(tasks):
    """Returns the next available ID for a new task"""
    if not tasks:
        return 1
    return max(task["id"] for task in tasks) + 1

datetime.now().isoformat() generates a sortable string in the format 2025-03-22T15:30:45.123456.

Sorting and Visual Indicators

Sorting is implemented without altering the original order of tasks in self.tasks. The get_sorted_tasks method returns a copy:

• First, incomplete tasks (completed == False)
• Then, completed tasks
• Within groups — by id

class TodoApp:
    
    def get_sorted_tasks(self):
        """Returns tasks sorted for display: active first, then completed"""
        active_tasks = [task for task in self.tasks if not task["completed"]]
        completed_tasks = [task for task in self.tasks if task["completed"]]
        active_tasks.sort(key=lambda x: x["id"])
        completed_tasks.sort(key=lambda x: x["id"])
        return active_tasks + completed_tasks

    def refresh_task_list(self):
        """Updates the task list display with sorting and color indicators"""
        self.task_listbox.delete(0, tk.END)
        sorted_tasks = self.get_sorted_tasks()

        for task in sorted_tasks:
            status = "✓" if task["completed"] else "○"
            try:
                created = datetime.fromisoformat(task["created_at"])
                date_str = created.strftime("%m/%d/%y %H:%M")
            except:
                date_str = "date unknown"

            display_text = f"{status} [{date_str}] {task['id']}. {task['text']}"

            self.task_listbox.insert(tk.END, display_text)

            bg_color = "white"
            fg_color = "black"

            if task["completed"]:
                fg_color = "green"
                bg_color = "light gray"
            else:
                if task["priority"] == "high":
                    fg_color = "red"
                    bg_color = "#ffe6e6"
                elif task["priority"] == "medium":
                    fg_color = "orange"
                    bg_color = "#fff0e6"

            index = tk.END
            self.task_listbox.itemconfig(tk.END, bg=bg_color, fg=fg_color)

Key techniques:

• itemconfig(index, bg=..., fg=...) for styling Listbox rows
• strftime("%m/%d/%y %H:%M") for localized date format
• Lazy sorting only during refresh_task_list

Modal Edit Window

Editing opens a Toplevel window with grab_set() for modality. The logic finds the task by id from the sorted list:

class TodoApp:
   def edit_task(self):
        selection = self.task_listbox.curselection()
        if not selection:
            messagebox.showwarning("Warning", "Select a task to edit")
            return

        selected_index = selection[0]
        sorted_tasks = self.get_sorted_tasks()
        selected_task = sorted_tasks[selected_index]
        task_id = selected_task["id"]

        task_to_edit = None
        task_index = None
        for i, task in enumerate(self.tasks):
            if task["id"] == task_id:
                task_to_edit = task
                task_index = i
                break

        if not task_to_edit:
            return

        edit_window = tk.Toplevel(self.root)
        edit_window.title(f"Editing Task #{task_id}")
        edit_window.geometry("450x250")
        edit_window.resizable(False, False)
        edit_window.grab_set()

        tk.Label(edit_window, text="Task Text:").pack(pady=(10, 0), anchor=tk.W, padx=10)
        text_entry = tk.Text(edit_window, height=4, width=50, font=("Arial", 10))
        text_entry.pack(pady=5, padx=10, fill=tk.BOTH, expand=True)
        text_entry.insert("1.0", task_to_edit["text"])

        tk.Label(edit_window, text="Priority:").pack(pady=(5, 0), anchor=tk.W, padx=10)
        priority_var = tk.StringVar(value=task_to_edit["priority"])
        priority_frame = tk.Frame(edit_window)
        priority_frame.pack(pady=5, padx=10, anchor=tk.W)

        tk.Radiobutton(priority_frame, text="High", variable=priority_var, value="high", fg="red").pack(side=tk.LEFT, padx=5)
        tk.Radiobutton(priority_frame, text="Medium", variable=priority_var, value="medium", fg="orange").pack(side=tk.LEFT, padx=5)
        tk.Radiobutton(priority_frame, text="Low", variable=priority_var, value="low").pack(side=tk.LEFT, padx=5)

        button_frame = tk.Frame(edit_window)
        button_frame.pack(pady=15)

        def save_edit():
            new_text = text_entry.get("1.0", "end-1c").strip()
            if not new_text:
                messagebox.showwarning("Warning", "Task text cannot be empty", parent=edit_window)
                return

            task_to_edit["text"] = new_text
            task_to_edit["priority"] = priority_var.get()
            save_tasks(self.tasks)
            self.refresh_task_list()
            edit_window.destroy()
            messagebox.showinfo("Success", f"Task #{task_id} updated")

        tk.Button(button_frame, text="Save", command=save_edit, bg="light green", width=10).pack(side=tk.LEFT, padx=5)
        tk.Button(button_frame, text="Cancel", command=edit_window.destroy, bg="light gray", width=10).pack(side=tk.LEFT, padx=5)

Integration: Add self.edit_button = tk.Button(bottom_frame, text="✏ Edit", command=self.edit_task) to create_widgets.

Add Task Dialog with Priority

The add_task method uses a similar Toplevel structure with focus on Entry and radio buttons:

• text_entry.focus() for UX
• Validation with strip() and emptiness check
• Auto-generation of id, created_at, completed=False

The full method code ensures consistency with editing.

Key Points

• Backward Compatibility: Automatic migration of created_at and priority on load
• Performance: Sorting a copy of the list, leaving persistent data untouched
• Listbox Styling: itemconfig(tk.END, bg=..., fg=...) for dynamic colors
• Modal Windows: Toplevel + grab_set() + resizable(False, False)
• Date Formatting: strftime for readable display of ISO strings

— Editorial Team