Terry Carroll wrote:
> I have a list (or a list-like object, doesn't matter) of objects, each of
> which has multiple fields. I want to be able to arbitrarily sort the list
> on any of them, or at least on several of them.
>
> To make this a little more concrete, here's a simplified idea. Say the
> objects each represent a file, and I've got fields in it
> like this:
>
> self.filesz: size of the file
> self.filename: name of the file
> self.users : a list of people who need to know if the file gets updated
> self.filetype : a short description of the file contents
>
> etc.
>
>
> I sometimes want to sort the list by filesz; and sometimes by filename;
> and maybe sometimes by some other field.
>
> My sense right now is that the "list" of these objects itself should be an
> object inheriting from list, and that I should create a small sort method
> for each field I intend to sort on. (I don't have the book handy, but
> there's a nice recipe for this in the Python Cookbook, 2d Edition, for
> such a method.)
As long as your list-like object is list-like enough to be sorted, you
can use operator.attrgetter to create functions that serve as a key
parameter.
In [1]: class foo(object):
...: def __init__(self, a, b, c):
...: self.a = a; self.b = b; self.c = c
...: def __repr__(self):
...: return repr((self.a, self.b, self.c))
...:
...:
In [2]: lst = [foo(1, 'one', 'I'), foo(2, 'two', 'II'), foo(10, 'ten',
'X'), foo(50, 'fifty', 'V')]
In [7]: lst
Out[7]: [(1, 'one', 'I'), (2, 'two', 'II'), (10, 'ten', 'X'), (50,
'fifty', 'V')]
In [8]: from operator import attrgetter
In [9]: lst.sort(key=attrgetter('b')); print lst
[(50, 'fifty', 'V'), (1, 'one', 'I'), (10, 'ten', 'X'), (2, 'two', 'II')]
In [10]: lst.sort(key=attrgetter('c')); print lst
[(1, 'one', 'I'), (2, 'two', 'II'), (50, 'fifty', 'V'), (10, 'ten', 'X')]
Kent
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