Split a file into sub files in python

Input file 'file.txt' is basically a log file containing running information of certain device interfaces in the following format:

$ cat file.txt
debug: on
max allowed connection: 3
tr#45
Starting: interface 78e23
Fan Status: On
Speed: -
sl no: 3431212-2323-90
vendor: aledaia
Stopping: interface 78e23
tr#90
newdebug received
Starting: interface 78e24
Fan Status: Off
Speed: 5670
sl no: 3431212-2323-90
vendor: aledaia
Stopping: interface 78e24
Starting: interface 68e73
Fan Status: On
Speed: 1200
sl no: 3431212-2323-90
vendor: aledaia
Stopping: interface 68e73
tr#99

Required:

Split the above file into sub-files such that
- Each sub file conatins information of an interface (basically information from 'Starting' and 'Stopping' of the interface)
- Sub-file name should be of the format: interface-name_someSLno.txt

The python script:

flag=0;c=0
for line in open("file.txt"):
    line=line.strip()
    if line.startswith("Stopping"):
        flag=0
        o.close()
    if line.startswith("Starting"):
        interface=line.split(" ")[2]
        flag=1;c=c+1
        o=open(interface+"_"+str(c)+".txt","w")
    if flag and not line.startswith("Starting"):
        print >>o, line

Output:

$ cat 78e23_1.txt
Fan Status: On
Speed: -
sl no: 3431212-2323-90
vendor: aledaia

$ cat 78e24_2.txt
Fan Status: Off
Speed: 5670
sl no: 3431212-2323-90
vendor: aledaia

$ cat 68e73_3.txt
Fan Status: On
Speed: 1200
sl no: 3431212-2323-90
vendor: aledaia