Chris Torek wrote:
> In article <iu00fs1...@news3.newsguy.com> I wrote, in part:
>>Another possible syntax:
>>
>> for item in container with key:
>>
>>which translates roughly to "bind both key and item to the value
>>for lists, but bind key to the key and value for the value for
>>dictionary-ish items". Then ... the OP would write, e.g.:
>>
>> for elem in sequence with index:
>> ...
>> sequence[index] = newvalue
>>
>>which of course calls the usual container.__setitem__. In this
>>case the "new protocol" is to have iterators define a function
>>that returns not just the next value in the sequence, but also
>>an appropriate "key" argument to __setitem__. For lists, this
>>is just the index; for dictionaries, it is the key; for other
>>containers, it is whatever they use for their keys.
>
> I note I seem to have switched halfway through thinking about
> this from "value" to "index" for lists, and not written that. :-)
>
> Here's a sample of a simple generator that does the trick for
> list, buffer, and dict:
>
> def indexed_seq(seq):
> """
> produce a pair
> <key_or_index> <value>
> such that seq[key_or_index] is <value> initially; you can
> write on seq[key_or_index] to set a new value while this
> operates. Note that we don't allow tuple and string here
> since they are not writeable.
> """
> if isinstance(seq, (list, buffer)):
> for i, v in enumerate(seq):
> yield i, v
> elif isinstance(seq, dict):
> for k in seq:
> yield k, seq[k]
> else:
> raise TypeError("don't know how to index %s" % type(seq))
>
> which shows that there is no need for a new syntax. (Turning the
> above into an iterator, and handling container classes that have
> an __iter__ callable that produces an iterator that defines an
> appropriate index-and-value-getter, is left as an exercise. :-) )
Here is what numpy nditer does:
for item in np.nditer(u, [], ['readwrite'], order='C'):
... item[...] = 10
Notice that the slice syntax is used to 'dereference' the iterator. This seems
like reasonably pythonic syntax, to my eye.
--
http://mail.python.org/mailman/listinfo/python-list
