Python xlrd.Book: how to close the files?

Question

I read 150 excel files in a loop, opening them with xlrd.open_workbook(), which returns a Book object. At the end, when I tried to umount the volume, I was unable, and when I checked with lsof, I found that 6 of the files were still open:

$ lsof | grep volumename

python2   32349         deeenes  mem       REG               0,40    138240     181517 /.../150119.xls
python2   32349         deeenes  mem       REG               0,40    135168     181482 /.../150609.xls
python2   32349         deeenes  mem       REG               0,40    140800     181495 /.../140828.xls
python2   32349         deeenes    5r      REG               0,40    140800     181495 /.../140828.xls
python2   32349         deeenes    6r      REG               0,40    135168     181482 /.../150609.xls
python2   32349         deeenes    7r      REG               0,40    138240     181517 /.../150119.xls

Here is my function I read the xls files with: (stripped for clarity)

import sys
import xlrd
from xlrd.biffh import XLRDError

def read_xls(xls_file, sheet = '', return_table = True):
    try:
        book = xlrd.open_workbook(xls_file, on_demand = True)
        try:
            sheet = book.sheet_by_name(sheet)
        except XLRDError:
            sheet = book.sheet_by_index(0)
        table = [[str(c.value) for c in sheet.row(i)] for i in xrange(sheet.nrows)]
        if not return_table:
            table = None
        return table
    except IOError:
        sys.stdout.write('No such file: %s\n' % xls_file)
    sys.stdout.flush()

The Book object does not have close() method, neither have any open file type objects among its properties, except the stdout. This howto does not tell about this (haven't found the official docs). I don't see how I could close the file, and also it is weird that 6 remains open after reading 150 of them.

Edit: it might be related to this, but still should not leave open files, and I don't want to read all sheets.

Answer 1

In case you open a workbook with on_demand = True for a more economic resource use (see here how does it work), you need to call release_resources() method at the end. As a minimal example:

import xlrd

book = xlrd.open_workbook('workbook.xls', on_demand = True)
sheet = book.sheet_by_index(0)
data = [[str(c.value) for c in sheet.row(i)] for i in xrange(sheet.nrows)]
book.release_resources()
del book