Create a GUI which divides a window into four panels, left to right and up to down.
To create a GUI in Python, you can use the Tkinter library, which comes pre-installed with Python. Below is an example code that creates a window that is divided into four panels:

```python
import tkinter as tk

root = tk.Tk()
root.geometry("400x400")

frame1 = tk.Frame(root, bg="red", bd=3)
frame1.place(relx=0.5, rely=0.25, relwidth=0.5, relheight=0.5, anchor='center')

frame2 = tk.Frame(root, bg="blue", bd=3)
frame2.place(relx=0.5, rely=0.75, relwidth=0.5, relheight=0.5, anchor='center')

frame3 = tk.Frame(root, bg="green", bd=3)
frame3.place(relx=0.25, rely=0.25, relwidth=0.5, relheight=0.5, anchor='center')

frame4 = tk.Frame(root, bg="yellow", bd=3)
frame4.place(relx=0.25, rely=0.75, relwidth=0.5, relheight=0.5, anchor='center')

root.mainloop()
```

In the above code, we first import the Tkinter library and create the main window by calling the `Tk` class' constructor. The `geometry` method is used to set the size of the window. 

Then, we create four frames which will represent the four panels of the window. Each frame is given a background color for distinction, and its size and position are set using the `place` method, which uses relative positioning. The `relx` and `rely` attributes specify the horizontal and vertical position of the frame, respectively, and the `relwidth` and `relheight` attributes specify the width and height of the frame, respectively.

Finally, we start the main event loop of the GUI by calling the `mainloop` method on the main window object.
Below is an instruction that describes a task, write a response that appropriately completes the request.

### Instruction:
Create a GUI which divides a window into four panels, left to right and up to down.

### Response:
To create a GUI in Python, you can use the Tkinter library, which comes pre-installed with Python. Below is an example code that creates a window that is divided into four panels:

```python
import tkinter as tk

root = tk.Tk()
root.geometry("400x400")

frame1 = tk.Frame(root, bg="red", bd=3)
frame1.place(relx=0.5, rely=0.25, relwidth=0.5, relheight=0.5, anchor='center')

frame2 = tk.Frame(root, bg="blue", bd=3)
frame2.place(relx=0.5, rely=0.75, relwidth=0.5, relheight=0.5, anchor='center')

frame3 = tk.Frame(root, bg="green", bd=3)
frame3.place(relx=0.25, rely=0.25, relwidth=0.5, relheight=0.5, anchor='center')

frame4 = tk.Frame(root, bg="yellow", bd=3)
frame4.place(relx=0.25, rely=0.75, relwidth=0.5, relheight=0.5, anchor='center')

root.mainloop()
```

In the above code, we first import the Tkinter library and create the main window by calling the `Tk` class' constructor. The `geometry` method is used to set the size of the window. 

Then, we create four frames which will represent the four panels of the window. Each frame is given a background color for distinction, and its size and position are set using the `place` method, which uses relative positioning. The `relx` and `rely` attributes specify the horizontal and vertical position of the frame, respectively, and the `relwidth` and `relheight` attributes specify the width and height of the frame, respectively.

Finally, we start the main event loop of the GUI by calling the `mainloop` method on the main window object.