[Tutor] Shelve del not reducing file size

[Barton David]

Hi,
 
I've hit a snag with Python's shelve module. By way of example...
 
_____
from shelve import DbfilenameShelf as StoreFile
import os
 
sf=StoreFile("mytest.db",writeback=False) # but same problem if
writeback=True
for i in range(10000):
    sf[str(i)]="TESTOBJECT"
sf.sync()
print len(sf)
sf.close()
predeletesize=os.path.getsize("mytest.db")
print predeletesize
 
sf=StoreFile("mytest.db",writeback=False) # but same problem if
writeback=True
for i in range(5000):
    del sf[str(i)]
sf.sync()
print len(sf)
sf.close()
postdeletesize=os.path.getsize("mytest.db")
print postdeletesize
_____
 
So why, when I run this, does predeletesize!=postdeletesize?
I gather that with most database types you have to invoke a special
command like VACUUM to perform cleanups after table deletions etc
so, since shelve uses database backends, is this related to that? Is
there a way to tell (e.g.) a DBfilenameShelf to do this? Or am I stuck
with having to delete the entire file and save it again?
 
 
Running PythonWin 2.5.1 on XP.
 
thanks
Dave

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