The code below gives you only the device ids.
import pprint
import subprocess
df = subprocess.check_output('lsusb', shell=True)
device_ids = []
for line in filter(lambda s: s.startswith('Bus'), df.split('\n')):
businfo, id, _ = line.split(':')
id = id.split()[1]
device_ids.append(id)
pprint.pprint(device_ids)