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Add a note reminding the reader that sets are not sequences. I

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received feedback that was based in the misunderstanding that sets
were sequences.
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Guido van Rossum 2002-08-20 20:05:23 +00:00
parent 0bd7832285
commit 290f1870f1
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10
Lib/sets.py
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@ -4,6 +4,16 @@ This module implements sets using dictionaries whose values are
ignored. The usual operations (union, intersection, deletion, etc.) ignored. The usual operations (union, intersection, deletion, etc.)
are provided as both methods and operators. are provided as both methods and operators.
Important: sets are not sequences! While they support 'x in s',
'len(s)', and 'for x in s', none of those operations are unique for
sequences; for example, mappings support all three as well. The
characteristic operation for sequences is subscripting with small
integers: s[i], for i in range(len(s)). Sets don't support
subscripting at all. Also, sequences allow multiple occurrences and
their elements have a definite order; sets on the other hand don't
record multiple occurrences and don't remember the order of element
insertion (which is why they don't support s[i]).
The following classes are provided: The following classes are provided:
BaseSet -- All the operations common to both mutable and immutable BaseSet -- All the operations common to both mutable and immutable