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Many small clarifications, including many suggested by email.

This commit is contained in:
Fred Drake 2000-09-19 18:10:05 +00:00
parent b96e0e5e65
commit 1156f62348
1 changed files with 18 additions and 17 deletions
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35
Doc/ref/ref5.tex
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@ -676,11 +676,10 @@ converted to a common type.
\section{Comparisons\label{comparisons}}
\index{comparison}
Contrary to \C, all comparison operations in Python have the same
priority, which is lower than that of any arithmetic, shifting or
bitwise operation. Also contrary to \C, expressions like
\code{a < b < c} have the interpretation that is conventional in
mathematics:
Unlike C, all comparison operations in Python have the same priority,
which is lower than that of any arithmetic, shifting or bitwise
operation. Also unlike C, expressions like \code{a < b < c} have the
interpretation that is conventional in mathematics:
\indexii{C}{language}
\begin{verbatim}
@ -708,11 +707,12 @@ perfectly legal (though perhaps not pretty).
The forms \code{<>} and \code{!=} are equivalent; for consistency with
C, \code{!=} is preferred; where \code{!=} is mentioned below
\code{<>} is also acceptable. At some point in the (far) future,
\code{<>} may become obsolete.
\code{<>} is also accepted. The \code{<>} spelling is considered
obsolescent.
The operators \texttt{"<", ">", "==", ">=", "<="}, and \texttt{"!="} compare
the values of two objects. The objects needn't have the same type.
The operators \code{<}, \code{>}, \code{==}, \code{>=}, \code{<=}, and
\code{!=} compare
the values of two objects. The objects need not have the same type.
If both are numbers, they are coverted to a common type. Otherwise,
objects of different types \emph{always} compare unequal, and are
ordered consistently but arbitrarily.
@ -732,7 +732,8 @@ Numbers are compared arithmetically.
\item
Strings are compared lexicographically using the numeric equivalents
(the result of the built-in function \function{ord()}) of their
characters.
characters. Unicode and 8-bit strings are fully interoperable in this
behavior.
\item
Tuples and lists are compared lexicographically using comparison of
@ -765,19 +766,19 @@ For the list, tuple 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.
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 the Unicode and string types, \code{\var{x} in \var{y}} is true if
and only if there exists an index \var{i} such that \code{\var{x} ==
\var{y}[\var{i}]} is true. If \code{\var{x}} is not a string or
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
do define \method{__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).