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| author | Raymond Hettinger <python@rcn.com> | 2005-04-10 17:32:35 (GMT) |
|---|---|---|
| committer | Raymond Hettinger <python@rcn.com> | 2005-04-10 17:32:35 (GMT) |
| commit | e490502e04f3c3847bd58183f4b6f284880c8709 (patch) | |
| tree | 7ae98dcefff005c126c03c886f83e2f3282d67ee /Doc/lib | |
| parent | 95ed80b0e06e9e5722c68e3054dad9177e20d449 (diff) | |
| download | cpython-e490502e04f3c3847bd58183f4b6f284880c8709.zip cpython-e490502e04f3c3847bd58183f4b6f284880c8709.tar.gz cpython-e490502e04f3c3847bd58183f4b6f284880c8709.tar.bz2 | |
SF bug #1179957: Missing def'n of equality for set elements
Diffstat (limited to 'Doc/lib')
| -rw-r--r-- | Doc/lib/libsets.tex | 5 | ||||
| -rw-r--r-- | Doc/lib/libstdtypes.tex | 3 |
2 files changed, 7 insertions, 1 deletions
diff --git a/Doc/lib/libsets.tex b/Doc/lib/libsets.tex index 8085ab1..0cd5e2e 100644 --- a/Doc/lib/libsets.tex +++ b/Doc/lib/libsets.tex @@ -30,7 +30,10 @@ method but omits methods which alter the contents of the set. Both abstract class useful for determining whether something is a set: \code{isinstance(\var{obj}, BaseSet)}. -The set classes are implemented using dictionaries. As a result, sets +The set classes are implemented using dictionaries. Accordingly, the +requirements for set elements are the same as those for dictionary keys; +namely, that the element defines both \method{__eq__} and \method{__hash__}. +As a result, sets cannot contain mutable elements such as lists or dictionaries. However, they can contain immutable collections such as tuples or instances of \class{ImmutableSet}. For convenience in implementing diff --git a/Doc/lib/libstdtypes.tex b/Doc/lib/libstdtypes.tex index c464517..03bccd9 100644 --- a/Doc/lib/libstdtypes.tex +++ b/Doc/lib/libstdtypes.tex @@ -1220,6 +1220,9 @@ Accordingly, sets do not implement the \method{__cmp__} method. Since sets only define partial ordering (subset relationships), the output of the \method{list.sort()} method is undefined for lists of sets. +Set elements are like dictionary keys; they need to define both +\method{__hash__} and \method{__eq__} methods. + Binary operations that mix \class{set} instances with \class{frozenset} return the type of the first operand. For example: \samp{frozenset('ab') | set('bc')} returns an instance of \class{frozenset}. |