[Python] Why does one work, but not the other?

You're probably doing something else wrong; this fragment works fine:
[[1], [2], [3], [4]]

----- Original Message -----
From: "j_mckitrick" <j_mckitrick at bigfoot.com>
Newsgroups: comp.lang.python
Sent: Thursday, June 17, 2004 9:54 PM
Subject: Why does one work, but not the other?

[1, 3, 2]
[1, 3, 2]

Check the dictionary, make sure it has entries?
When supplying the dictionary with elements given by the list, make sure the
keys exist.

or you can do:
Will return None if a key does not exist to further debug.

Hope this helps.

Adonis

Thanks for the help, guys. I found the problem. The liststore cannot
be redefined once set up for the TreeView. I can only clear/append to
it.

But I'm still on my mission to replace 'for' with list comprehensions
where possible, according to the article on optimization on the python
site.


That being said, is there a way to write this as a comprehension? I
can't figure out how to do so and get k into the key correctly. I'm
just trying to save a dictionary via anydbm.

for k, v in self.options.items():
db[k] = str(v)

jonathon

I don't know the article, but I assume it doesn't tell list comprehensions
are always faster/better.
Yes,
{1: '4', 2: '6', 3: '8'}
>>>

but why would you trade a muddy comprehension for a clean loop? The for loop
is clearer (and faster, I suppose) here. Remember that list comprehensions
are a means rather than an end.

With 2.4 that may be a different story, as the above will reduce (I think)
to

dk.update((k, str(v)) for (k, v) in options.iteritems())

However, some overhead (generating throwaway tuples) is likely to remain.

Peter

Peter Otten <__peter__ at web.de> wrote in message news:<cauk4d$b4n$00$1 at news.t-online.com>...
from http://www.python.org/doc/essays/list2str.html:

Try to use map(), filter() or reduce() to replace an explicit for
loop, but only if you can use a built-in function: map with a built-in
function beats for loop, but a for loop with in-line code beats map
with a lambda function!


I remember another, but can't find it right now.

Dunno--I don't get an empty list.
[[1], [2], [3]]

Seems the problem lies elsewhere...


Robert Brewer
MIS
Amor Ministries
fumanchu at amor.org

"j_mckitrick" <j_mckitrick at bigfoot.com> wrote in message
news:ec6dce8b.0406171754.5d5d84db at posting.google.com...
For questions like this, about supposedly anomalous behavior, you usually
need to give actual input and output, reduced to the minimum code needed to
show the purported behavior. Otherwise, the easiest guess is that you did
not use the same value of data in the two snippets;-)

Terry J. Reedy

My usual solution to that is generically written:

dict([(k, v) for k, v in d.iteritems()])

...taking advantage of the fact the you can pass dict() a list of
tuples. Your specific example would be written:

db = dict([(k, str(v)) for k, v in self.options.iteritems()])

I use iteritems more often, since it doesn't create an intermediate
structure.


Robert Brewer
MIS
Amor Ministries
fumanchu at amor.org

P.S. Where is everyone on c.l.p. today? Brother Ray's memorial...?