Python - extract blocks of data from file

Input file contains addresses of 3 persons:

$ cat details.txt
Details:Mr X
Koramangala Post
3rd Cross, 17th Main
PIN: 12345
Details:Mr Y:details
NGV
PIN: 45678
Details:Mr Z:details
5th Ave, #23
NHM Post
LKV
PIN: 32456

Output required: We are required to divide/split the above file into 3 sub-files, each should contain one address.
The python program:

f=0
for line in open("details.txt"):
    line=line.strip()
    if "Details" in line:
        filename=line.split(":")[1]
        o=open(filename.replace(" ","_"),"w")
        f=1
    if f:print >>o, line

Output: Sub-files generated after execution of the above program:

$ cat Mr_X
Details:Mr X
Koramangala Post
3rd Cross, 17th Main
PIN: 12345

$ cat Mr_Y
Details:Mr Y:details
NGV
PIN: 45678

$ cat Mr_Z
Details:Mr Z:details
5th Ave, #23
NHM Post
LKV
PIN: 32456

- Related solution using awk from my bash scripting blog