slicing does not work on Python 2.4: deepcopy fails with TypeError due to function attribute _sort_key

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Run tests on Python 2.4

What is the expected output? What do you see instead?
Tests should pass. Instead, slicing tests fail:

+ /usr/bin/python prettytable_test.py
...............................EE...
======================================================================
ERROR: testSliceFirstTwoRows (__main__.SlicingTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "prettytable_test.py", line 192, in testSliceFirstTwoRows
    y = self.x[0:2]
  File "/builddir/build/BUILD/prettytable-0.6.1/prettytable.py", line 171, in __getitem__
    newtable = copy.deepcopy(self)
  File "/usr/lib64/python2.4/copy.py", line 204, in deepcopy
    y = _reconstruct(x, rv, 1, memo)
  File "/usr/lib64/python2.4/copy.py", line 351, in _reconstruct
    state = deepcopy(state, memo)
  File "/usr/lib64/python2.4/copy.py", line 174, in deepcopy
    y = copier(x, memo)
  File "/usr/lib64/python2.4/copy.py", line 268, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib64/python2.4/copy.py", line 204, in deepcopy
    y = _reconstruct(x, rv, 1, memo)
  File "/usr/lib64/python2.4/copy.py", line 336, in _reconstruct
    y = callable(*args)
  File "/usr/lib64/python2.4/copy_reg.py", line 92, in __newobj__
    return cls.__new__(cls, *args)
TypeError: function() takes at least 2 arguments (0 given)
======================================================================
ERROR: testSliceLastTwoRows (__main__.SlicingTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "prettytable_test.py", line 201, in testSliceLastTwoRows
    y = self.x[-2:]
  File "/builddir/build/BUILD/prettytable-0.6.1/prettytable.py", line 171, in __getitem__
    newtable = copy.deepcopy(self)
  File "/usr/lib64/python2.4/copy.py", line 204, in deepcopy
    y = _reconstruct(x, rv, 1, memo)
  File "/usr/lib64/python2.4/copy.py", line 351, in _reconstruct
    state = deepcopy(state, memo)
  File "/usr/lib64/python2.4/copy.py", line 174, in deepcopy
    y = copier(x, memo)
  File "/usr/lib64/python2.4/copy.py", line 268, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib64/python2.4/copy.py", line 204, in deepcopy
    y = _reconstruct(x, rv, 1, memo)
  File "/usr/lib64/python2.4/copy.py", line 336, in _reconstruct
    y = callable(*args)
  File "/usr/lib64/python2.4/copy_reg.py", line 92, in __newobj__
    return cls.__new__(cls, *args)
TypeError: function() takes at least 2 arguments (0 given)
----------------------------------------------------------------------
Ran 36 tests in 0.050s
FAILED (errors=2)

What version of the product are you using? On what operating system?
prettytable-0.6.1, python-2.4.3 (RHEL5)

Please provide any additional information below.
This patch fixes the test suite, and it should be safe to use None because 
.sort() accepts None for the key. But I think it will still break if the caller 
slices a PrettyTable with a custom sort_key set on it. It might be necessary to 
write a custom __deepcopy__ or avoid using deepcopy.

diff -ur prettytable-0.6.1.orig/prettytable.py 
prettytable-0.6.1.patched/prettytable.py
--- prettytable-0.6.1.orig/prettytable.py   2012-06-04 08:22:23.000000000 +1000
+++ prettytable-0.6.1.patched/prettytable.py    2013-11-19 08:26:01.231044684 +1000
@@ -137,7 +137,7 @@

         self._sortby = kwargs["sortby"] or None
         self._reversesort = kwargs["reversesort"] or False
-        self._sort_key = kwargs["sort_key"] or (lambda x: x)
+        self._sort_key = kwargs["sort_key"]

         self._int_format = kwargs["float_format"] or {}
         self._float_format = kwargs["float_format"] or {}

Original issue reported on code.google.com by dan...@gmail.com on 18 Nov 2013 at 10:31

[GoogleCodeExporter]

Hi there.  Thanks for pointing this out.  I assume you are stuck using 2.4 for 
your application for some reason?

Original comment by luke@maurits.id.au on 24 Nov 2013 at 7:25

[GoogleCodeExporter]

Right, we are still supporting back to RHEL5 which has Python 2.4.

Original comment by dan...@gmail.com on 25 Nov 2013 at 3:34