[ python-Bugs-1721372 ] emphasize iteration volatility for set

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Bugs item #1721372, was opened at 2007-05-18 17:10
Message generated for change (Comment added) made by loewis
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Category: Documentation
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Alan (aisaac0)
Assigned to: Nobody/Anonymous (nobody)
Summary: emphasize iteration volatility for set

Initial Comment:
For <URL:http://docs.python.org/lib/types-set.html>, append the following new sentence to the 2nd paragraph.

    Iteration over a set returns elements in an indeterminate order, which generally depends on factors outside the scope of the containing program.

*Justification:* users should not be expected to understand without being told that iteration order depends on factors outside the scope of the containing program. (Additionally, unlike the documentation for dictionaries, the documentation for sets fails to give a serious warning not to rely on iteration order.)


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>Comment By: Martin v. Löwis (loewis)
Date: 2007-05-18 19:05

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What factors outside the containing program influence iteration order?
Iteration is completely deterministic, and only depends on the items
inserted, and the order in which they were inserted, neither of which is
outside the scope of the containing program. It's just that the order is
not easily predictable.

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