In [1]:

    

import sys
sys.version


    

    
Out[1]:





'2.7.6 (default, Mar 22 2014, 22:59:56) \n[GCC 4.8.2]'

In [2]:

    

from builtins import object


    

In [2]:

    

object??


    

In [3]:

    

# Py3-style iterators written as new-style classes (subclasses of
# future.builtins.object) are backward compatibile with Py2:
class Upper(object):
    def __init__(self, iterable):
        self._iter = iter(iterable)
    def __next__(self):                 # note the Py3 interface
        return next(self._iter).upper()
    def __iter__(self):
        return self


    

In [5]:

    

assert list(Upper('hello')) == list('HELLO')


    

In [6]:

    

class AllOrNothing(object):
    def __init__(self, l):
        self.l = l
    def __bool__(self):
        return all(self.l)


    

In [8]:

    

container = AllOrNothing([0, 100, 200])
bool(container)


    

    
Out[8]:





False

In [9]:

    

container2 = AllOrNothing([-100, 100, 200])
bool(container2)


    

    
Out[9]:





True

In [13]:

    

class AllOrNothingBroken(list):
    def __bool__(self):
        print('Called!')
        return all(self)


    

In [14]:

    

container3 = AllOrNothingBroken([0, 1, 2])
bool(container3)


    

    
Out[14]:





True

In [15]:

    

from builtins import list

class AllOrNothingFixed(list):
    def __bool__(self):
        print('Called!')
        return all(self)


    

In [17]:

    

container4 = AllOrNothingFixed([0, 1, 2])
bool(container4)


    

    
Out[17]:





True

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