Excise the sets module. SF #1500611 by Collin Winter.

1 files changed, 0 insertions, 264 deletions

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-\section{\module{sets} ---
-         Unordered collections of unique elements}
-
-\declaremodule{standard}{sets}
-\modulesynopsis{Implementation of sets of unique elements.}
-\moduleauthor{Greg V. Wilson}{gvwilson@nevex.com}
-\moduleauthor{Alex Martelli}{aleax@aleax.it}
-\moduleauthor{Guido van Rossum}{guido@python.org}
-\sectionauthor{Raymond D. Hettinger}{python@rcn.com}
-
-\versionadded{2.3}
-
-The \module{sets} module provides classes for constructing and manipulating
-unordered collections of unique elements.  Common uses include membership
-testing, removing duplicates from a sequence, and computing standard math
-operations on sets such as intersection, union, difference, and symmetric
-difference.
-
-Like other collections, sets support \code{\var{x} in \var{set}},
-\code{len(\var{set})}, and \code{for \var{x} in \var{set}}.  Being an
-unordered collection, sets do not record element position or order of
-insertion.  Accordingly, sets do not support indexing, slicing, or
-other sequence-like behavior.
-
-Most set applications use the \class{Set} class which provides every set
-method except for \method{__hash__()}. For advanced applications requiring
-a hash method, the \class{ImmutableSet} class adds a \method{__hash__()}
-method but omits methods which alter the contents of the set. Both
-\class{Set} and \class{ImmutableSet} derive from \class{BaseSet}, an
-abstract class useful for determining whether something is a set:
-\code{isinstance(\var{obj}, BaseSet)}.
-
-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
-sets of sets, inner sets are automatically converted to immutable
-form, for example, \code{Set([Set(['dog'])])} is transformed to
-\code{Set([ImmutableSet(['dog'])])}.
-
-\begin{classdesc}{Set}{\optional{iterable}}
-Constructs a new empty \class{Set} object.  If the optional \var{iterable}
-parameter is supplied, updates the set with elements obtained from iteration.
-All of the elements in \var{iterable} should be immutable or be transformable
-to an immutable using the protocol described in
-section~\ref{immutable-transforms}.
-\end{classdesc}
-
-\begin{classdesc}{ImmutableSet}{\optional{iterable}}
-Constructs a new empty \class{ImmutableSet} object.  If the optional
-\var{iterable} parameter is supplied, updates the set with elements obtained
-from iteration.  All of the elements in \var{iterable} should be immutable or
-be transformable to an immutable using the protocol described in
-section~\ref{immutable-transforms}.
-
-Because \class{ImmutableSet} objects provide a \method{__hash__()} method,
-they can be used as set elements or as dictionary keys.  \class{ImmutableSet}
-objects do not have methods for adding or removing elements, so all of the
-elements must be known when the constructor is called.
-\end{classdesc}
-
-
-\subsection{Set Objects \label{set-objects}}
-
-Instances of \class{Set} and \class{ImmutableSet} both provide
-the following operations:
-
-\begin{tableiii}{c|c|l}{code}{Operation}{Equivalent}{Result}
-  \lineiii{len(\var{s})}{}{cardinality of set \var{s}}
-
-  \hline
-  \lineiii{\var{x} in \var{s}}{}
-         {test \var{x} for membership in \var{s}}
-  \lineiii{\var{x} not in \var{s}}{}
-         {test \var{x} for non-membership in \var{s}}
-  \lineiii{\var{s}.issubset(\var{t})}{\code{\var{s} <= \var{t}}}
-         {test whether every element in \var{s} is in \var{t}}
-  \lineiii{\var{s}.issuperset(\var{t})}{\code{\var{s} >= \var{t}}}
-         {test whether every element in \var{t} is in \var{s}}
-
-  \hline
-  \lineiii{\var{s}.union(\var{t})}{\var{s} \textbar{} \var{t}}
-         {new set with elements from both \var{s} and \var{t}}
-  \lineiii{\var{s}.intersection(\var{t})}{\var{s} \&\ \var{t}}
-         {new set with elements common to \var{s} and \var{t}}
-  \lineiii{\var{s}.difference(\var{t})}{\var{s} - \var{t}}
-         {new set with elements in \var{s} but not in \var{t}}
-  \lineiii{\var{s}.symmetric_difference(\var{t})}{\var{s} \^\ \var{t}}
-         {new set with elements in either \var{s} or \var{t} but not both}
-  \lineiii{\var{s}.copy()}{}
-         {new set with a shallow copy of \var{s}}
-\end{tableiii}
-
-Note, the non-operator versions of \method{union()},
-\method{intersection()}, \method{difference()}, and
-\method{symmetric_difference()} will accept any iterable as an argument.
-In contrast, their operator based counterparts require their arguments to
-be sets.  This precludes error-prone constructions like
-\code{Set('abc') \&\ 'cbs'} in favor of the more readable
-\code{Set('abc').intersection('cbs')}.
-\versionchanged[Formerly all arguments were required to be sets]{2.3.1}
-
-In addition, both \class{Set} and \class{ImmutableSet}
-support set to set comparisons.  Two sets are equal if and only if
-every element of each set is contained in the other (each is a subset
-of the other).
-A set is less than another set if and only if the first set is a proper
-subset of the second set (is a subset, but is not equal).
-A set is greater than another set if and only if the first set is a proper
-superset of the second set (is a superset, but is not equal).
-
-The subset and equality comparisons do not generalize to a complete
-ordering function.  For example, any two disjoint sets are not equal and
-are not subsets of each other, so \emph{all} of the following return
-\code{False}:  \code{\var{a}<\var{b}}, \code{\var{a}==\var{b}}, or
-\code{\var{a}>\var{b}}.
-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.
-
-The following table lists operations available in \class{ImmutableSet}
-but not found in \class{Set}:
-
-\begin{tableii}{c|l}{code}{Operation}{Result}
-  \lineii{hash(\var{s})}{returns a hash value for \var{s}}
-\end{tableii}
-
-The following table lists operations available in \class{Set}
-but not found in \class{ImmutableSet}:
-
-\begin{tableiii}{c|c|l}{code}{Operation}{Equivalent}{Result}
-  \lineiii{\var{s}.update(\var{t})}
-         {\var{s} \textbar= \var{t}}
-         {return set \var{s} with elements added from \var{t}}
-  \lineiii{\var{s}.intersection_update(\var{t})}
-         {\var{s} \&= \var{t}}
-         {return set \var{s} keeping only elements also found in \var{t}}
-  \lineiii{\var{s}.difference_update(\var{t})}
-         {\var{s} -= \var{t}}
-         {return set \var{s} after removing elements found in \var{t}}
-  \lineiii{\var{s}.symmetric_difference_update(\var{t})}
-         {\var{s} \textasciicircum= \var{t}}
-         {return set \var{s} with elements from \var{s} or \var{t}
-          but not both}
-
-  \hline
-  \lineiii{\var{s}.add(\var{x})}{}
-         {add element \var{x} to set \var{s}}
-  \lineiii{\var{s}.remove(\var{x})}{}
-         {remove \var{x} from set \var{s}; raises \exception{KeyError}
-	  if not present}
-  \lineiii{\var{s}.discard(\var{x})}{}
-         {removes \var{x} from set \var{s} if present}
-  \lineiii{\var{s}.pop()}{}
-         {remove and return an arbitrary element from \var{s}; raises
-	  \exception{KeyError} if empty}
-  \lineiii{\var{s}.clear()}{}
-         {remove all elements from set \var{s}}
-\end{tableiii}
-
-Note, the non-operator versions of \method{update()},
-\method{intersection_update()}, \method{difference_update()}, and
-\method{symmetric_difference_update()} will accept any iterable as
-an argument.
-\versionchanged[Formerly all arguments were required to be sets]{2.3.1}
-
-Also note, the module also includes a \method{union_update()} method
-which is an alias for \method{update()}.  The method is included for
-backwards compatibility.  Programmers should prefer the
-\method{update()} method because it is supported by the builtin
-\class{set()} and \class{frozenset()} types.
-
-\subsection{Example \label{set-example}}
-
-\begin{verbatim}
->>> from sets import Set
->>> engineers = Set(['John', 'Jane', 'Jack', 'Janice'])
->>> programmers = Set(['Jack', 'Sam', 'Susan', 'Janice'])
->>> managers = Set(['Jane', 'Jack', 'Susan', 'Zack'])
->>> employees = engineers | programmers | managers           # union
->>> engineering_management = engineers & managers            # intersection
->>> fulltime_management = managers - engineers - programmers # difference
->>> engineers.add('Marvin')                                  # add element
->>> print engineers
-Set(['Jane', 'Marvin', 'Janice', 'John', 'Jack'])
->>> employees.issuperset(engineers)           # superset test
-False
->>> employees.union_update(engineers)         # update from another set
->>> employees.issuperset(engineers)
-True
->>> for group in [engineers, programmers, managers, employees]:
-...     group.discard('Susan')                # unconditionally remove element
-...     print group
-...
-Set(['Jane', 'Marvin', 'Janice', 'John', 'Jack'])
-Set(['Janice', 'Jack', 'Sam'])
-Set(['Jane', 'Zack', 'Jack'])
-Set(['Jack', 'Sam', 'Jane', 'Marvin', 'Janice', 'John', 'Zack'])
-\end{verbatim}
-
-
-\subsection{Protocol for automatic conversion to immutable
-            \label{immutable-transforms}}
-
-Sets can only contain immutable elements.  For convenience, mutable
-\class{Set} objects are automatically copied to an \class{ImmutableSet}
-before being added as a set element.
-
-The mechanism is to always add a hashable element, or if it is not
-hashable, the element is checked to see if it has an
-\method{__as_immutable__()} method which returns an immutable equivalent.
-
-Since \class{Set} objects have a \method{__as_immutable__()} method
-returning an instance of \class{ImmutableSet}, it is possible to
-construct sets of sets.
-
-A similar mechanism is needed by the \method{__contains__()} and
-\method{remove()} methods which need to hash an element to check
-for membership in a set.  Those methods check an element for hashability
-and, if not, check for a \method{__as_temporarily_immutable__()} method
-which returns the element wrapped by a class that provides temporary
-methods for \method{__hash__()}, \method{__eq__()}, and \method{__ne__()}.
-
-The alternate mechanism spares the need to build a separate copy of
-the original mutable object.
-
-\class{Set} objects implement the \method{__as_temporarily_immutable__()}
-method which returns the \class{Set} object wrapped by a new class
-\class{_TemporarilyImmutableSet}.
-
-The two mechanisms for adding hashability are normally invisible to the
-user; however, a conflict can arise in a multi-threaded environment
-where one thread is updating a set while another has temporarily wrapped it
-in \class{_TemporarilyImmutableSet}.  In other words, sets of mutable sets
-are not thread-safe.
-
-
-\subsection{Comparison to the built-in \class{set} types
-            \label{comparison-to-builtin-set}}
-
-The built-in \class{set} and \class{frozenset} types were designed based
-on lessons learned from the \module{sets} module.  The key differences are:
-
-\begin{itemize}
-\item \class{Set} and \class{ImmutableSet} were renamed to \class{set} and
-      \class{frozenset}.
-\item There is no equivalent to \class{BaseSet}.  Instead, use
-      \code{isinstance(x, (set, frozenset))}.
-\item The hash algorithm for the built-ins performs significantly better
-      (fewer collisions) for most datasets.
-\item The built-in versions have more space efficient pickles.
-\item The built-in versions do not have a \method{union_update()} method.
-      Instead, use the \method{update()} method which is equivalent.
-\item The built-in versions do not have a \method{_repr(sorted=True)} method.
-      Instead, use the built-in \function{repr()} and \function{sorted()}
-      functions:  \code{repr(sorted(s))}.
-\item The built-in version does not have a protocol for automatic conversion
-      to immutable.  Many found this feature to be confusing and no one
-      in the community reported having found real uses for it.
-\end{itemize}