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Moshe Zadka <mzadka@geocities.com>: 

Update the "in" / "not in" description to accomodate the current use
of the __contains__() discipline.  This patch also incorporates
suggestions from Marc-Andre Lemburg <mal@lemburg.com>, minor markup
revisions from Fred Drake, and some rewording of the first affected
paragraph (also from Fred).

Closes SourceForge patch #100831.
This commit is contained in:
Fred Drake 2000-07-11 19:43:47 +00:00
parent 85f363990c
commit 7399b9e6e4
1 changed files with 29 additions and 8 deletions
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37
Doc/ref/ref5.tex
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@ -740,14 +740,35 @@ execution of a program.
\end{itemize} \end{itemize}
The operators \keyword{in} and \keyword{not in} test for sequence The operators \keyword{in} and \keyword{not in} test for set
membership: if \var{y} is a sequence, \code{\var{x} in \var{y}} is membership: every type can define membership in whatever way is
true if and only if there exists an index \var{i} such that appropriate. Traditionally, this interface has been tightly bound
\code{\var{x} = \var{y}[\var{i}]}. the sequence interface, which is related in that presence in a sequence
\code{\var{x} not in \var{y}} yields the inverse truth value. The can be usefully interpreted as membership in a set.
exception \exception{TypeError} is raised when \var{y} is not a sequence,
or when \var{y} is a string and \var{x} is not a string of length For the list, tuple types, \code{\var{x} in \var{y}} is true if and only
one.\footnote{The latter restriction is sometimes a nuisance.} if there exists such an index \var{i} such that
\code{var{x} == \var{y}[\var{i}]} is true.
For the Unicode and string types, \code{\var{x} in \var{y}} is true if and only
if there exists such an index \var{i} such that
\code{var{x} == \var{y}[\var{i}]} is true. If \code{\var{x}} is not
a string of length \code{1} or a unicode object of length \code{1},
a \exception{TypeError} exception is raised.
For user-defined classes which define the \method{__contains__()} method,
\code{\var{x} in \var{y}} is true if and only if
\code{\var{y}.__contains__(\var{x})} is true.
For user-defined classes which do not define \method{__contains__()} and
do define \var{__getitem__}, \code{\var{x} in \var{y}} is true if and only
if there is a non-negative integer index \var{i} such that
\code{\var{x} == \var{y}[\var{i}]}, and all lower integer indices
do not raise \exception{IndexError} exception. (If any other exception
is raised, it is as if \keyword{in} raised that exception).
The operator \keyword{not in} is defined to have the inverse true value
of \keyword{in}.
\opindex{in} \opindex{in}
\opindex{not in} \opindex{not in}
\indexii{membership}{test} \indexii{membership}{test}