Dino Viehland wrote:
Interesting, the docs would seem to indicate our behavior is correct:
For user-defined classes which do not define __contains__() and do define
__getitem__(), x in y is true if and only if there is a non-negative integer
index i such that x == y[i], and all lower integer indices do not raise
IndexError exception. (If any other exception is raised, it is as if in raised
that exception).
If and only if is pretty strong language ☺ But we can start looking for
__iter__ after looking for __contains__.
It sounds like a doc bug then.
'in' has different meanings for mapping type containers (in refers to
keys) and sequences (in refers to values). For a sequence 'in' naturally
and obviously means 'is a value contained in the sequence', and passing
the value to __getitem__ clearly gives the wrong behaviour.
For mapping types, passing the value to __getitem__ would be correct -
unfortunately there is no way to tell the types of containers apart if
they are pure Python classes (except in Python 2.6 where we have
Abstract Base Classes). Explicitly implementing __contains__ is always
better than relying on the fallback.
Michael
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Glenn Jones
Sent: Thursday, November 20, 2008 7:23 AM
To: [email protected]
Subject: [IronPython] in operator calls __getitem__ on class that has __len__
and __iter__ defined
Yet another weirdness, but not a blocker for us:
With this object:
class o(object):
def __iter__(self):
print "iter"
return iter([1, 2, 3])
def __getitem__(self, index):
print "getitem"
return [1, 2, 3][index]
def __len__(self):
print "len"
return 3
CPython:
p = o()
1 in p
iter
True
IronPython 2 source drop 43741:
p = o()
1 in p
getitem
True
It looks like CPython is treating it like a sequence and IronPython 2 is
treating it like a dict.
We have worked around this by implementing __contains__
Raised as Issue 19678 on CodePlex.
PS: How can we format code blocks on CodePlex?
Glenn & Orestis
_______________________________________________
Users mailing list
[email protected]
http://lists.ironpython.com/listinfo.cgi/users-ironpython.com
--
http://www.ironpythoninaction.com/
_______________________________________________
Users mailing list
[email protected]
http://lists.ironpython.com/listinfo.cgi/users-ironpython.com
