Python "IOError: [Errno 22] Invalid argument" when using cPickle to write large array to network drive

Question

EDIT: At the suggestion of J. F. Sebastian, I can get the same error much more simply:

Python 2.6.4 (r264:75708, Oct 26 2009, 08:23:19) [MSC v.1500 32 bit (Intel)]
Type "copyright", "credits" or "license" for more information.

IPython 0.10 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object'. ?object also works, ?? prints more.

  Welcome to pylab, a matplotlib-based Python environment.
  For more information, type 'help(pylab)'.

In [1]: open(r'c:\test.bin', 'wb').write('a'*67076095)

In [2]: open(r'c:\test.bin', 'wb').write('a'*67076096)

In [3]: open(r'z:\test.bin', 'wb').write('a'*67076095)

In [4]: open(r'z:\test.bin', 'wb').write('a'*67076096)
---------------------------------------------------------------------------
IOError                                   Traceback (most recent call last)

C:\Documents and Settings\User\<ipython console> in <module>()

IOError: [Errno 22] Invalid argument

In [5]:

Note that C: is a local drive, and Z: is a network drive.

ORIGINAL QUESTION:

Python 2.6.4 on Windows XP crashes if I use cPickle to write a file bigger than ~67 MB to our network drive (ReadyNAS Pro Pioneer edition). I'd like to be able to pickle large files. Is this a known problem? Is there a workaround?

The following script produces a crash:

import cPickle, numpy

a = numpy.zeros(8385007)
print "Writing %i bytes..."%(a.nbytes)
cPickle.dump(a, open('test_a.pkl', 'wb'), protocol=2)
print "Successfully written."

b = numpy.zeros(8385008)
print "Writing %i bytes..."%(b.nbytes)
cPickle.dump(b, open('test_b.pkl', 'wb'), protocol=2) ##Crashes on a network drive
print "Successfully written." ##Doesn't crash on a non-network drive

Here's the steps I take to produce a crash at the ipython prompt:

Python 2.6.4 (r264:75708, Oct 26 2009, 08:23:19) [MSC v.1500 32 bit (Intel)]
Type "copyright", "credits" or "license" for more information.

IPython 0.10 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object'. ?object also works, ?? prints more.

  Welcome to pylab, a matplotlib-based Python environment.
  For more information, type 'help(pylab)'.

In [1]: pwd
Out[1]: 'C:\\Documents and Settings\\User'

In [2]: run test
Writing 67080056 bytes...
Successfully written.
Writing 67080064 bytes...
Successfully written.

In [3]: cd Z:
Z:\

In [4]: pwd
Out[4]: 'Z:\\'

In [5]: run 'C:\\Documents and Settings\\User\\test'
Writing 67080056 bytes...
Successfully written.
Writing 67080064 bytes...
---------------------------------------------------------------------------
IOError                                   Traceback (most recent call last)

C:\Documents and Settings\User\test.py in <module>()
      8 b = numpy.zeros(8385008)
      9 print "Writing %i bytes..."%(b.nbytes)
---> 10 cPickle.dump(b, open('test_b.pkl', 'wb'), protocol=2)
     11 print "Successfully written."
     12

IOError: [Errno 22] Invalid argument
WARNING: Failure executing file: <C:\\Documents and Settings\\User\\test.py>

In [6]:

C: is the local hard drive on the machine. Z: is our network-attached storage.

Solution

I believe the problem is related to: http://support.microsoft.com/default.aspx?scid=kb;en-us;899149

...so, just try: open(r'z:\test.bin','w+b').write('a'*67080064)

*Note the argument: 'w+b'

Comments

[Andrew]

open(r'z:\test.bin', 'wb').write('a'*67076096) fails, wheras open(r'z:\test.bin', 'wb').write('a'*67076095) doesn't fail, but is too small. Luckily, open(r'z:\test.bin', 'w+b').write('a'*67076096) works!

[Serendipity]

Doesn't work for Mac OS X. The patch that fixes this is under review for a long time bugs.python.org/issue24658