How do I make shelve file empty in python?

Question

I have created a shelve file and inserted a dictionary data. Now I want to cleanup that shelve file to reuse as a clean file.

import shelve
dict = shelve.open("Sample.db")
# insert some data into sample.db
dict = { "foo" : "bar"}

#Now I want to clean entire shelve file to re-insert the data from begining.

Answer 1

dict.clear() is the easiest, and should be valid, but seems to not actually clear the shelf files (Python 3.5.2, Windows 7 64-bit). For example, the shelf .dat file size grows every time I run the following snippet, while I would expect it to always have the same size:

shelf = shelve.open('shelf')
shelf.clear()
shelf['0'] = list(range(10000))
shelf.close()

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Update: dbm.dumb, which shelve uses as its underlying database under Windows, contains this TODO item in its code:

• reclaim free space (currently, space once occupied by deleted or expanded items is never reused)

This explains the ever-growing shelf file problem.

---

So instead of dict.clear(), I'm using shelve.open with flag='n'. Quoting shelve.open() documentation:

The optional flag parameter has the same interpretation as the flag parameter of dbm.open().

And dbm.open() documentation for flag='n':

Always create a new, empty database, open for reading and writing

If the shelf is already open, the usage would be:

shelf.close()
shelf = shelve.open('shelf', flag='n')