How to layout two buttons in verticle by PySimpleGUI?

Question

I use code as below to set layout, I want to two buttons in vertical not in horizontal, what can I do?

layout = [
    [
        sg.Input(readonly=True, expand_x=True, key='Main', disabled_readonly_background_color=sg.theme_input_background_color()),
        sg.Button("Select Folder")
    ],
    [
        sg.Frame("Subfolders & Files", frame_subholders), 
        sg.Button(' ← '), sg.Button(' → '),
        sg.Frame("Selected files", frame_selected)
    ],

Answer 1

As @Jason says, you can use sg.Column. This is a complete working example based on your layout:

import PySimpleGUI as sg

frame_subholders = [[sg.Multiline()]]
frame_selected = [[sg.Multiline()]]

column = [
    [sg.Button(' ← ')],
    [sg.Button(' → ')]
]

layout = [
    [sg.Input("", readonly=True, expand_x=True),
    sg.Button('Select Folder')],
    [
        sg.Frame("Subfolders & Files", frame_subholders),
        sg.Column(column),
        sg.Frame("Selected files", frame_selected)
    ]]

window = sg.Window('Test', layout)

while True:
    event, values = window.read()
    if event == sg.WINDOW_CLOSED:
        break
    if event == 'Select Folder':
        print('Button pressed')

window.close()