Implement, test and document "key in dict" and "key not in dict".
I know some people don't like this -- if it's really controversial,
I'll take it out again. (If it's only Alex Martelli who doesn't like
it, that doesn't count as "real controversial" though. :-)
That's why this is a separate checkin from the iterators stuff I'm
about to check in next.
diff --git a/Doc/ref/ref3.tex b/Doc/ref/ref3.tex
index 1f3afbf..adb619a 100644
--- a/Doc/ref/ref3.tex
+++ b/Doc/ref/ref3.tex
@@ -1134,7 +1134,10 @@
\method{__add__()}, \method{__radd__()}, \method{__iadd__()},
\method{__mul__()}, \method{__rmul__()} and \method{__imul__()} described
below; they should not define \method{__coerce__()} or other numerical
-operators.
+operators. It is recommended that both mappings and sequences
+implement the \method{__contains__}, to allow efficient use of the
+\code{in} operator; for mappings, \code{in} should be equivalent of
+\method{has_key()}; for sequences, it should search through the values.
\withsubitem{(mapping object method)}{
\ttindex{keys()}
\ttindex{values()}
@@ -1143,7 +1146,8 @@
\ttindex{get()}
\ttindex{clear()}
\ttindex{copy()}
- \ttindex{update()}}
+ \ttindex{update()}
+ \ttindex{__contains__()}}
\withsubitem{(sequence object method)}{
\ttindex{append()}
\ttindex{count()}
@@ -1158,7 +1162,8 @@
\ttindex{__iadd__()}
\ttindex{__mul__()}
\ttindex{__rmul__()}
- \ttindex{__imul__()}}
+ \ttindex{__imul__()}
+ \ttindex{__contains__()}}
\withsubitem{(numeric object method)}{\ttindex{__coerce__()}}
\begin{methoddesc}[mapping object]{__len__}{self}
diff --git a/Doc/ref/ref5.tex b/Doc/ref/ref5.tex
index 5663daa..ec0c6b1 100644
--- a/Doc/ref/ref5.tex
+++ b/Doc/ref/ref5.tex
@@ -768,7 +768,9 @@
The set membership test has traditionally been bound to sequences; an
object is a member of a set if the set is a sequence and contains an
element equal to that object. However, it is possible for an object
-to support membership tests without being a sequence.
+to support membership tests without being a sequence. In particular,
+dictionaries support memership testing as a nicer way of spelling
+\code{\var{key} in \var{dict}}; other mapping types may follow suit.
For the list and tuple types, \code{\var{x} in \var{y}} is true if and
only if there exists an index \var{i} such that