Python program doesn't quit when finished

Question

I have the following script 186.py:

S=[]
study=set([524287])

tmax=10**7
D={}
DF={}
dudcount=0
callcount=0

def matchval(t1,t2):
    if t1==t2:
        global dudcount
        dudcount+=1
    else:
        global callcount
        callcount+=1
        D.setdefault(t1,set([]))
        D.setdefault(t2,set([]))
        D[t1].add(t2)
        if t1 in D[t2]:
            DF.setdefault(t1,set([]))
            DF[t1].add(t2)
            DF.setdefault(t2,set([]))
            DF[t2].add(t1)

for k in xrange(27):
    t1=(100003 - 200003*(2*k+1) + 300007*(2*k+1)**3)%(1000000)
    S.append(t1)
    t2=(100003 - 200003*(2*k+2) + 300007*(2*k+2)**3)%(1000000)
    S.append(t2)
    matchval(t1,t2)

t1=(100003 - 200003*(55) + 300007*(55)**3)%(1000000)
S.append(t1)
t2=(S[31]+S.pop(0))%(1000000)
S.append(t2)
matchval(t1,t2)

for k in xrange(29,tmax+1):
    t1=(S[31]+S.pop(0))%(1000000)
    S.append(t1)

    t2=(S[31]+S.pop(0))%(1000000)
    S.append(t2)
    matchval(t1,t2)

D.setdefault(524287,set([]))
DF.setdefault(524287,set([]))
print D[524287]
print DF[524287]
print dudcount,callcount
print "Done"

The last line prints "Done" but python doesn't exit when this happens. I type the following command:

$ time python 186.py

And get the results:

set([810528L, 582178L, 49419L, 214483L, 974071L, 651738L, 199163L, 193791L])
set([])
11 9999989
Done

But I have to ctrl+C to get the time:

real    34m18.642s
user    2m26.465s
sys     0m11.645s

After the program outputs "Done" python CPU usage is very little... but the memory usage continues to grow... I used ctrl+C once it got to 80% of my system memory (its an old system).

What is going on here? What is the program doing after Done is printed? Shouldn't it be done?

Thanks, Dan

Answer 1

I ran the same code on my 2 GHz dual-core laptop with 2GB RAM and it took about 1 1/2 minutes in Cygwin. The memory usage got up over 600 MB before the program quit and it took about 2-4 seconds after Done appeared for the prompt to come up and the memory to be released. However, I didn't see any memory increase after the Done appeared.

My guess is it has to do with memory management. After the Done appears, Python is working on freeing all of the memory which might take quite a while on an older machine with less RAM. I'm not sure why the memory actually increases unless there is just a delay in whatever is telling you how much memory is being used.