If you don't want the second do_smth2() to run if first do_smth1() worked, then just add the second try under the first except. If do_smth1() worked, then do_smth2() will not be tried.
try:
x=do_smth1()
except:
try:
x=do_smth2()
except:
x="Both Failed"
print ("Both Failed"x)