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Diffstat (limited to 'Doc/ref')
| -rw-r--r-- | Doc/ref/ref3.tex | 37 |
1 files changed, 36 insertions, 1 deletions
diff --git a/Doc/ref/ref3.tex b/Doc/ref/ref3.tex index 7eddfcd..fb57eb0 100644 --- a/Doc/ref/ref3.tex +++ b/Doc/ref/ref3.tex @@ -378,6 +378,41 @@ additional example of a mutable sequence type. \end{description} % Sequences + +\item[Set types] +These represent unordered, finite sets of unique, immutable objects. +As such, they cannot be indexed by any subscript. However, they can be +iterated over, and the built-in function \function{len()} returns the +number of items in a set. Common uses for sets are +fast membership testing, removing duplicates from a sequence, and +computing mathematical operations such as intersection, union, difference, +and symmetric difference. +\bifuncindex{len} +\obindex{set type} + +For set elements, the same immutability rules apply as for dictionary +keys. Note that numeric types obey the normal rules for numeric +comparison: if two numbers compare equal (e.g., \code{1} and +\code{1.0}), only one of them can be contained in a set. + +There are currently two intrinsic set types: + +\begin{description} + +\item[Sets] +These\obindex{set} represent a mutable set. They are created by the +built-in \function{set()} constructor and can be modified afterwards +by several methods, such as \method{add()}. + +\item[Frozen sets] +These\obindex{frozenset} represent an immutable set. They are created by +the built-in \function{frozenset()} constructor. As a frozenset is +immutable and hashable, it can be used again as an element of another set, +or as a dictionary key. + +\end{description} % Set types + + \item[Mappings] These represent finite sets of objects indexed by arbitrary index sets. The subscript notation \code{a[k]} selects the item indexed @@ -761,7 +796,7 @@ user-defined method object whose associated class is the class (call it~\class{C}) of the instance for which the attribute reference was initiated or one of its bases, it is transformed into a bound user-defined method object whose -\member{im_class} attribute is~\class{C} whose \member{im_self} attribute +\member{im_class} attribute is~\class{C} and whose \member{im_self} attribute is the instance. Static method and class method objects are also transformed, as if they had been retrieved from class~\class{C}; see above under ``Classes''. See section~\ref{descriptors} for |