[Pytables-users] File instances and WeakValueDictionaries

[<AF...@pr...>]

	I have a class that reads data from a number of HDF5 files, and to save 
time opening them, I'm trying to use a WeakValueDictionary as a simple 
cache.  But File objects seem to have more references than just the 
label returned from openFile.

In [1]: import weakref

In [2]: import tables

In [3]: cache = weakref.WeakValueDictionary()

In [4]: fyle = tables.openFile('Foo-1990.h5')

In [5]: import sys

In [6]: sys.getrefcount(fyle)
Out[6]: 6

In [9]: cache[0] = fyle

In [10]: sys.getrefcount(fyle)
Out[10]: 6

In [11]: del fyle

In [12]: cache.keys()
Out[12]: [0]

In [13]: sys.getrefcount(cache.values()[0])
Out[13]: 5

	(In this example 'Foo-1990.h5' has roughly 250 Arrays, all off the root 
group, but I've opened up files with only three arrays and gotten even 
higher refcounts.)

	I've checked to see whether PyTables is caching the file instances, but 
repeated calls to tables.openFile return different objects.

	What is holding these references?  What is the proper way to completely 
remove a File object?

-- 
Anthony Foglia
Princeton Consultants
(609) 987-8787 x233