On 03/06/17 21:10, Jon Forrest wrote: > I'm learning about Python. A book I'm reading about it > says "... a string in Python is a sequence. A sequence is an ordered > collection of objects". This implies that each character in a string > is itself an object. > > This doesn't seem right to me, but since I'm just learning Python > I questioned the author about this. He gave an example the displays > the ids of string slices. These ids are all different, but I think > that's because the slicing operation creates objects. > > I'd like to suggest an explanation of what a sequence is > that doesn't use the word 'object' because an object has > a specific meaning in Python. > > Am I on the right track here?
No, strings don't internally store the characters as objects, and yes, the slicing operation creates objects. However, strings *are* sequences, sequences *are* ordered collections of objects. The sentence "A sequence is an ordered collection of objects" means that a sequence has (ordered) elements, you can access these elements, and when you do that, you will get an object (seeing as everything is an object). It does *not* imply that all the elements of a sequence exist in memory before you access them. This definition of a sequence describes the behaviour, not the implementation, of a sequence object. Another built-in sequence type that doesn't bother to store all of its elements as objects, or at all, is range: >>> r = range(1000000000) # Does NOT create one billion objects >>> i = r[10000] # The element is an object. >>> i 10000 >>> id(i) 139758670321552 >>> i is 10000 False >>> NB: in Python 2, range does store all of its elements as objects. Running this code in Python 2 will consume many gigabytes of memory. If you have to use Python 2, use xrange instead. Hope this helps. Thomas -- https://mail.python.org/mailman/listinfo/python-list
