var = StringVar()
os.chdir('C:\Users\mhoban')
all_subdirs = [d for d in os.listdir('.') if os.path.isdir(d)]
for dirs in all_subdirs:
    dir = os.path.join('C:\Users\mhoban', dirs)
    os.chdir(dir)
    current = os.getcwd()
    new = str(current).split("\")[3]

opt1 = OptionMenu(app, var, new)
opt1.grid(row=0, column=1, padx=10, pady=10)
opt1.configure(width = 40, bg = "White")