The following DevFS files will provide this information:
/proc/net/arp
/proc/net/route
Find the route entry with 0/0 as the host/mask:
Iface Destination Gateway Flags RefCnt Use Metric Mask MTU Window IRTT
eth0 00000000 B91A210A 0003 0 0 100 00000000 0 0 0
and convert the Gateway field (it's in little-endian hex... grr):
import struct
from IPy import IP
address = IP(struct.unpack('<I', struct.pack('>I', int(i, 16)))[0])
#Converts 'B91A210A' to IP('10.33.26.185')
From there, you can find your default gateway in the arp table:
IP address HW type Flags HW address Mask Device
10.33.26.185 0x1 0x2 e6:92:ec:f5:af:f7 * eth0
If it doesn't show up, issue a single ping, then check again, then fail.