Geek Answers Handbook

Defining __repr__ when subclasses are defined in Python

I am trying to subclass an object setin Python using code similar to the one below, but I cannot use a reasonable definition __repr__to use.

class Alpha(set):
    def __init__(self, name, s=()):
        super(Alpha, self).__init__(s)
        self.name = name

I would like to define __repr__in such a way as to get the following result:

>>> Alpha('Salem', (1,2,3))
Alpha('Salem', set([1, 2, 3]))

However, if I do not override __repr__, the output that I get ignores the value name...

>>> Alpha('Salem', (1,2,3))
Alpha([1, 2, 3])

... while, if I override __repr__, I cannot directly access the values ​​in the set without creating a new instance of the set:

class Alpha(set):
    …
    def __repr__(self):
        return "%s(%r, %r)" % (self.__class__.__name__, self.name, set(self))

This works, but creating a new instance of the set for __repr__, which will then be deleted, seems awkward and inefficient for me.

__repr__ ?

. , : . , ( - __repr__ - ), .

class Alpha(set):
    def __init__(self, name, s=()):
        super(Alpha, self).__init__(s)
        self.name = name
        self._set = set(s)
    def __repr__(self):
        return "%s(%r, %r)" % (self.__class__.__name__, self.name, self._set)
+5
2

, -, , , . , , .

#!/usr/bin/env python

import time

class Alpha(set):
    def __init__(self, name, s=()):
            super(Alpha, self).__init__(s)
            self.name = name
    def __repr__(self):
            return '%s(%r, set(%r))' % (self.__class__.__name__, 
                                        self.name, 
                                        list(self))

class Alpha2(set):
    def __init__(self, name, s=()):
            super(Alpha2, self).__init__(s)
            self.name = name
    def __repr__(self):
            return '%s(%r, set(%r))' % (self.__class__.__name__, 
                                        self.name, 
                                        set(self))

class Alpha3(set):
    def __init__(self, name, s=()):
            super(Alpha3, self).__init__(s)
            self.name = name
    def __repr__(self):
            rep = super(Alpha3, self).__repr__()
            rep = rep.replace(self.__class__.__name__, 'set', 1)
            return '%s(%r, %s)' % (self.__class__.__name__, 
                                    self.name, 
                                    rep)

def timeit(exp, repeat=10000):
    results = []
    for _ in xrange(repeat):
        start = time.time()
        exec(exp)
        end = time.time()-start
        results.append(end*1000)
    return sum(results) / len(results)

if __name__ == "__main__":
    print "Alpha():  ", timeit("a = Alpha('test', (1,2,3,4,5))")
    print "Alpha2(): ", timeit("a = Alpha2('test', (1,2,3,4,5))")
    print "Alpha3(): ", timeit("a = Alpha3('test', (1,2,3,4,5))")

:

(): 0.0287627220154

Alpha2(): 0.0286467552185

Alpha3(): 0,0285225152969

+7

, . , , .

(Python 2.x)

>>> class Alpha(set):
...     def __init__(self, name, s=()):
...             super(Alpha, self).__init__(s)
...             self.name = name
...     def __repr__(self):
...             return 'Alpha(%r, set(%r))' % (self.name, list(self))
... 
>>> Alpha('test', (1, 2))
Alpha('test', set([1, 2]))

, hardcoded ( ).

>>> class Alpha(set):
...     def __init__(self, name, s=()):
...             super(Alpha, self).__init__(s)
...             self.name = name
...     def __repr__(self):
...             return '%s(%r, set(%r))' % (self.__class__.__name__, self.name, list(self))
... 
>>> Alpha('test', (1, 2))
Alpha('test', set([1, 2]))
+2

More articles:


All Articles