dict.keys() ?

[bearophileHUGS@lycos.com]

The PEP 3100:

http://www.python.org/dev/peps/pep-3100/

says:

Return iterators instead of lists where appropriate for atomic type
methods (e.g. dict.keys(), dict.values(), dict.items(), etc.); iter*
methods will be removed. Better: make keys(), etc. return views ala
Java collections???
....
To be removed:
dict.setdefault ()? [15]
dict.has_key() method [done]


I may be sleepy now, but maybe the keys() method too can be removed;
otherwise the following two become really the same:

print list(adict)
for k in adict: ...

print list(adict.keys ())
for k in adict.keys(): ...

Bye,
bearophile

[George Sakkis]

Re: dict.keys() ?

On Jan 26, 10:04 pm, bearophileH...@ lycos.com wrote:

The PEP 3100:http://www.python.org/dev/peps/pep-3100/
says:
>
Return iterators instead of lists where appropriate for atomic type
methods (e.g. dict.keys(), dict.values(), dict.items(), etc.); iter*
methods will be removed. Better: make keys(), etc. return views ala
Java collections???
...
To be removed:
dict.setdefault ()? [15]
dict.has_key() method [done]
>
I may be sleepy now, but maybe the keys() method too can be removed;
otherwise the following two become really the same:
>
print list(adict)
for k in adict: ...
>
print list(adict.keys ())
for k in adict.keys(): ...

Alas, the consensus has moved away from simple iterators to less
lightweight "views":

http://svn.python.org/view/peps/trunk/pep-3106.txt?rev=53096&view=markup

"The objects returned by the .keys() and .items() methods behave like
sets with limited mutability; the allow removing elements, but not
adding them.(...) The object returned by the values() method behaves
like a multiset."

I for one am not convinced that adding three new types is worth the
complexity and the error-proneness of having two new
similar-but-not-quite-the-same APIs with sets. Not only iteration is
arguably the most common operation on a view, but the cost (in extra
keystrokes and runtime performance) of populating any container that
the user may need from an iterator is pretty low.

George