Confused about the output from set() in Python(2.4.3)

Question

I am a beginner in python and I am using python 2.4.3.

I have a question regarding to the order resulted from the set()function.

I understand set() will remove the the duplicate elements from a string and

[class set([iterable])

Return a new set object, optionally with elements taken from iterable.]1

But for example, when I do the following

a='abcdabcd' 
set(a)

it returned a result of

set(['a','c','b','d'])

in stead of

set(['a','b','c','d'])

which I would actually expect.

Why is that? I am not able to understand how the output was generated.

Many thanks in advance.

Also possibly relevant: http://stackoverflow.com/q/12165200/748858 — mgilson, Jul 14 '16 at 23:01
any referral documentation regarding the "unordered collection"? — Meruemu, Jul 14 '16 at 23:03
@Meruemu -- Have a look [here](https://docs.python.org/2/library/sets.html#module-sets) (Notice the banner title). Admittedly, that's for python2.7, but it still applies to python2.4 — mgilson, Jul 14 '16 at 23:04
for those who wondering, there are many universities use historical systems...and software never updates... — Meruemu, Jul 14 '16 at 23:09
@Meruemu, well if you want to learn python I would recommend getting a newer version to play with. — Padraic Cunningham, Jul 14 '16 at 23:12

score 0 · Accepted Answer · answered Jul 14 '16 at 22:57

0

A set is defined as an "unordered collection of unique elements" (see here). The set object in Python make no guarantees about ordering, and you should not expect nor rely on the order to stay the same.

answered Jul 14 '16 at 22:57

Erik Godard

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I think that this is _mostly_ correct, but it does make one (sometimes useful) guarantee about the order -- specifically, multiple iterations over the same set will yield items in the same order provided that you haven't added or removed any items. – mgilson Jul 14 '16 at 23:02

Confused about the output from set() in Python(2.4.3)

1 Answers1