Python List Iterator Comparison Demo

python_list_iterator_comparison.py

# copy, paste, and execute this code in a python repl with python v2.7.12 or greater installed
import sys; assert sys.version_info >= (2,7,12)

# reimplement default repr function to return a module, name, and memory address of given object
def __repr__(self):
    return '<%s.%s object at %s>' % (
        self.__class__.__module__,
        self.__class__.__name__,
        hex(id(self))
    )

# assume accepts array of numbers as parameters
def normalise_defensive(numbers):
        print("list iterator at memory addresses: {}, {}".format( iter(nums), iter(nums) ) )
        print("list iterator same id: {}, {}".format( id(iter(nums)), id(iter(nums)) ) )
        print("list iterator memory addresses: {}, {}".format(iter(nums).__repr__(), iter(nums).__repr__()))
        if iter(numbers) is iter(numbers): # An iterator -- bad!
                # unreachable as iterators point to different memory addresses
                raise TypeError('Must supply a container')

normalise_defensive([1,2])