[Tutor] Sorting Instance Attributes

[Magnus Lycka]

At 21:40 2002-12-11 -0600, Don Arnold wrote:
>This got me to thinking (which can be dangerous at times): what if you don't
>always want to sort by the same attribute? I played around a little, and
>here's what I came up with:
>
>def setStudentKey(key):
>     """builds the comparison function on the fly"""
>     c = 'def studentCompare(l,r):\n\treturn cmp(str(l.%s),str(r.%s))\n' \
>         % (key, key)
>     exec(c,__builtins__.__dict__)

Another approach would be to do something like this:

 >>> class Student:
...    compare = 'lname'
...    def __init__(self, fname, lname):
...        self.fname = fname
...        self.lname = lname
...    def __str__(self):
...        return "%s %s" % (self.fname, self.lname)
...    def setStudentKey(self, attribute):
...        if attribute not in self.__dict__.keys():
...            return AttributeError
...        Student.compare = attribute
...    def __cmp__(self, other):
...        return cmp(getattr(self, Student.compare),
...                    getattr(other, Student.compare))
...
 >>> a = Student('Allan', 'Zak')
 >>> b = Student('Barney', 'Yak')
 >>> c = Student('Caesar', 'Xak')
 >>> l = [a,b,c]
 >>> l.sort()
 >>> map(str, l)
['Caesar Xak', 'Barney Yak', 'Allan Zak']
 >>> b.setStudentKey('fname')
 >>> l.sort()
 >>> map(str, l)
['Allan Zak', 'Barney Yak', 'Caesar Xak']
 >>> a.setStudentKey('lname')
 >>> l.sort()
 >>> map(str, l)
['Caesar Xak', 'Barney Yak', 'Allan Zak']
 >>>


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Magnus Lycka, Thinkware AB
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