pop_r0_r1_r2_r3_pc

[umerov1999]

print '[*] pop_r0_r1_r2_r3_pc : 0x{:08x}'.format(pop_r0_r1_r2_r3_pc)
ValueError: Unknown format code 'x' for object of type 'str'

How replace pop {r0, r1, r2, r3, pc}?