On Nov 3, 6:49 pm, George Sakkis <[EMAIL PROTECTED]> wrote:
> I want to sort sequences of strings lexicographically but those with
> longer prefix should come earlier, e.g. for s = ['a', 'bc', 'bd',
> 'bcb', 'ba', 'ab'], the sorted sequence is ['ab', 'a', 'ba', 'bcb',
> 'bc', 'bd']. Currently I do it with:
>
> s.sort(cmp=lambda x,y: 0 if x==y else
> -1 if x.startswith(y) else
> +1 if y.startswith(x) else
> cmp(x,y))
>
> Can this be done with an equivalent key function instead of cmp ?
>
> George
Your input and output:
s = ['a', 'bc', 'bd', 'bcb', 'ba', 'ab']
r = ['ab', 'a', 'ba', 'bcb', 'bc', 'bd']
To me your lambda looks like an abuse of the inline if expression. So
I suggest to replace it with a true function, that is more readable:
def mycmp(x, y):
if x == y:
return 0
elif x.startswith(y):
return -1
elif y.startswith(x):
return +1
else:
return cmp(x, y)
print sorted(s, cmp=mycmp)
It's a peculiar cmp function, I'm thinking still in what situations it
can be useful.
To use the key argument given a cmp function I use the simple code
written by Hettinger:
def cmp2key(mycmp):
"Converts a cmp= function into a key= function"
class K:
def __init__(self, obj, *args):
self.obj = obj
def __cmp__(self, other):
return mycmp(self.obj, other.obj)
return K
print sorted(s, key=cmp2key(mycmp))
Now I'll look for simpler solutions...
Bye,
bearophile
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