How to find the max object as per some custom criterion?

I can do max(s) to find the max of a sequence. But suppose I want 开发者_如何学Pythonto compute max according to my own function, something like:

currmax = 0
def mymax(s):
  for i in s :
    #assume arity() attribute is present
    currmax = i.arity() if i.arity() > currmax else currmax

Is there a clean pythonic way of doing this?

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max(s, key=operator.methodcaller('arity'))

or

max(s, key=lambda x: x.arity())

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For instance,

max (i.arity() for i in s)

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You can still use the max function:

max_arity = max(s, key=lambda i: i.arity())

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I think the generator expression of doublep is better, but we seldom get to use methodcaller, so...

from operator import methodcaller
max(map(methodcaller('arity'), s))