LazyCat.__getitem__() called via __repr__() cripples LazyCat.__add__()

[Sean Upton]

You can add LazyCats together, but only before __repr__() is called or an instance is cast to another sequence type: __getitem__() removes self._seq on line 106 of r40218 in HEAD. To duplicate:

>>> from Products.ZCatalog.Lazy import LazyCat
>>> lazy1 = LazyCat([ [1,2], ])
>>> lazy1._seq
[[1, 2]]
>>> lazy1 += LazyCat([ [3,4], ])
>>> lazy1._seq
[[1, 2], [3, 4]]
>>> print lazy1 # __repr__ casts to list, calls getitem, removes lazy1._seq
[1, 2, 3, 4]
>>> lazy1._seq #this is bad
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
AttributeError: LazyCat instance has no attribute '_seq'
>>> lazy1 += LazyCat([ [5,6], ]) #this fails because of this bug!
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/home/upton/eg/swhome/lib/python/Products/ZCatalog/Lazy.py", line 43, in __add__
    return LazyCat([self, other])
  File "/home/upton/eg/swhome/lib/python/Products/ZCatalog/Lazy.py", line 68, in __init__
    flattened_seq.extend(s._seq)
AttributeError: LazyCat instance has no attribute '_seq'

[Sean Upton (seanupton)]

agreed - I'll write a test tomorrow and submit patch with test added to tests/testLazySequences.py

[Sean Upton (seanupton)]

Uploaded: fix-for-2326.diff

Fix / patch attached as diff to latest svn://svn.zope.org/repos/main/Zope/trunk/lib/python/Products/ZCatalog.

Call to _seq is avoided in __init__() when adding LazyCats together, working around the way that __getitem__() is implemented. Appears to work correctly:

>>> lazy1 = LazyCat( [ [1,2] ] )
>>> lazy1 += LazyCat( [ [3,4] ])
>>> lazy1
[1, 2, 3, 4]
>>> lazy1 += LazyCat( [ [3,4] ])
>>> lazy1
[1, 2, 3, 4, 3, 4]

[Andreas Jung (ajung)]

The patch requires a unittest.

[Tres Seaver (tseaver)]

Constructing a test from the code in the description should be trivial.

[Hanno Schlichting (hannosch)]

This was fixed in r121708 for Products.ZCatalog, released in 2.13.14 (2011-05-19).