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-\chapter{Expressions and conditions}
-\index{expression}
-\index{condition}
-
-{\bf Note:} In this and the following chapters, extended BNF notation
-will be used to describe syntax, not lexical analysis.
-\index{BNF}
-
-This chapter explains the meaning of the elements of expressions and
-conditions.  Conditions are a superset of expressions, and a condition
-may be used wherever an expression is required by enclosing it in
-parentheses.  The only places where expressions are used in the syntax
-instead of conditions is in expression statements and on the
-right-hand side of assignment statements; this catches some nasty bugs
-like accidentally writing \verb@x == 1@ instead of \verb@x = 1@.
-\indexii{assignment}{statement}
-
-The comma plays several roles in Python's syntax.  It is usually an
-operator with a lower precedence than all others, but occasionally
-serves other purposes as well; e.g. it separates function arguments,
-is used in list and dictionary constructors, and has special semantics
-in \verb@print@ statements.
-\index{comma}
-
-When (one alternative of) a syntax rule has the form
-
-\begin{verbatim}
-name:           othername
-\end{verbatim}
-
-and no semantics are given, the semantics of this form of \verb@name@
-are the same as for \verb@othername@.
-\index{syntax}
-
-\section{Arithmetic conversions}
-\indexii{arithmetic}{conversion}
-
-When a description of an arithmetic operator below uses the phrase
-``the numeric arguments are converted to a common type'',
-this both means that if either argument is not a number, a
-\verb@TypeError@ exception is raised, and that otherwise
-the following conversions are applied:
-\exindex{TypeError}
-\indexii{floating point}{number}
-\indexii{long}{integer}
-\indexii{plain}{integer}
-
-\begin{itemize}
-\item	first, if either argument is a floating point number,
-	the other is converted to floating point;
-\item	else, if either argument is a long integer,
-	the other is converted to long integer;
-\item	otherwise, both must be plain integers and no conversion
-	is necessary.
-\end{itemize}
-
-\section{Atoms}
-\index{atom}
-
-Atoms are the most basic elements of expressions.  Forms enclosed in
-reverse quotes or in parentheses, brackets or braces are also
-categorized syntactically as atoms.  The syntax for atoms is:
-
-\begin{verbatim}
-atom:      identifier | literal | enclosure
-enclosure: parenth_form|list_display|dict_display|string_conversion
-\end{verbatim}
-
-\subsection{Identifiers (Names)}
-\index{name}
-\index{identifier}
-
-An identifier occurring as an atom is a reference to a local, global
-or built-in name binding.  If a name is assigned to anywhere in a code
-block (even in unreachable code), and is not mentioned in a
-\verb@global@ statement in that code block, then it refers to a local
-name throughout that code block.  When it is not assigned to anywhere
-in the block, or when it is assigned to but also explicitly listed in
-a \verb@global@ statement, it refers to a global name if one exists,
-else to a built-in name (and this binding may dynamically change).
-\indexii{name}{binding}
-\index{code block}
-\stindex{global}
-\indexii{built-in}{name}
-\indexii{global}{name}
-
-When the name is bound to an object, evaluation of the atom yields
-that object.  When a name is not bound, an attempt to evaluate it
-raises a \verb@NameError@ exception.
-\exindex{NameError}
-
-\subsection{Literals}
-\index{literal}
-
-Python knows string and numeric literals:
-
-\begin{verbatim}
-literal:        stringliteral | integer | longinteger | floatnumber
-\end{verbatim}
-
-Evaluation of a literal yields an object of the given type (string,
-integer, long integer, floating point number) with the given value.
-The value may be approximated in the case of floating point literals.
-See section \ref{literals} for details.
-
-All literals correspond to immutable data types, and hence the
-object's identity is less important than its value.  Multiple
-evaluations of literals with the same value (either the same
-occurrence in the program text or a different occurrence) may obtain
-the same object or a different object with the same value.
-\indexiii{immutable}{data}{type}
-
-(In the original implementation, all literals in the same code block
-with the same type and value yield the same object.)
-
-\subsection{Parenthesized forms}
-\index{parenthesized form}
-
-A parenthesized form is an optional condition list enclosed in
-parentheses:
-
-\begin{verbatim}
-parenth_form:      "(" [condition_list] ")"
-\end{verbatim}
-
-A parenthesized condition list yields whatever that condition list
-yields.
-
-An empty pair of parentheses yields an empty tuple object.  Since
-tuples are immutable, the rules for literals apply here.
-\indexii{empty}{tuple}
-
-(Note that tuples are not formed by the parentheses, but rather by use
-of the comma operator.  The exception is the empty tuple, for which
-parentheses {\em are} required --- allowing unparenthesized ``nothing''
-in expressions would cause ambiguities and allow common typos to
-pass uncaught.)
-\index{comma}
-\indexii{tuple}{display}
-
-\subsection{List displays}
-\indexii{list}{display}
-
-A list display is a possibly empty series of conditions enclosed in
-square brackets:
-
-\begin{verbatim}
-list_display:   "[" [condition_list] "]"
-\end{verbatim}
-
-A list display yields a new list object.
-\obindex{list}
-
-If it has no condition list, the list object has no items.  Otherwise,
-the elements of the condition list are evaluated from left to right
-and inserted in the list object in that order.
-\indexii{empty}{list}
-
-\subsection{Dictionary displays} \label{dict}
-\indexii{dictionary}{display}
-
-A dictionary display is a possibly empty series of key/datum pairs
-enclosed in curly braces:
-\index{key}
-\index{datum}
-\index{key/datum pair}
-
-\begin{verbatim}
-dict_display:   "{" [key_datum_list] "}"
-key_datum_list: key_datum ("," key_datum)* [","]
-key_datum:      condition ":" condition
-\end{verbatim}
-
-A dictionary display yields a new dictionary object.
-\obindex{dictionary}
-
-The key/datum pairs are evaluated from left to right to define the
-entries of the dictionary: each key object is used as a key into the
-dictionary to store the corresponding datum.
-
-Restrictions on the types of the key values are listed earlier in
-section \ref{types}.
-Clashes between duplicate keys are not detected; the last
-datum (textually rightmost in the display) stored for a given key
-value prevails.
-\exindex{TypeError}
-
-\subsection{String conversions}
-\indexii{string}{conversion}
-\indexii{reverse}{quotes}
-\indexii{backward}{quotes}
-\index{back-quotes}
-
-A string conversion is a condition list enclosed in reverse (or
-backward) quotes:
-
-\begin{verbatim}
-string_conversion: "`" condition_list "`"
-\end{verbatim}
-
-A string conversion evaluates the contained condition list and
-converts the resulting object into a string according to rules
-specific to its type.
-
-If the object is a string, a number, \verb@None@, or a tuple, list or
-dictionary containing only objects whose type is one of these, the
-resulting string is a valid Python expression which can be passed to
-the built-in function \verb@eval()@ to yield an expression with the
-same value (or an approximation, if floating point numbers are
-involved).
-
-(In particular, converting a string adds quotes around it and converts
-``funny'' characters to escape sequences that are safe to print.)
-
-It is illegal to attempt to convert recursive objects (e.g. lists or
-dictionaries that contain a reference to themselves, directly or
-indirectly.)
-\obindex{recursive}
-
-The built-in function \verb@repr()@ performs exactly the same
-conversion in its argument as enclosing it it reverse quotes does.
-The built-in function \verb@str()@ performs a similar but more
-user-friendly conversion.
-\bifuncindex{repr}
-\bifuncindex{str}
-
-\section{Primaries} \label{primaries}
-\index{primary}
-
-Primaries represent the most tightly bound operations of the language.
-Their syntax is:
-
-\begin{verbatim}
-primary:        atom | attributeref | subscription | slicing | call
-\end{verbatim}
-
-\subsection{Attribute references}
-\indexii{attribute}{reference}
-
-An attribute reference is a primary followed by a period and a name:
-
-\begin{verbatim}
-attributeref:   primary "." identifier
-\end{verbatim}
-
-The primary must evaluate to an object of a type that supports
-attribute references, e.g. a module or a list.  This object is then
-asked to produce the attribute whose name is the identifier.  If this
-attribute is not available, the exception \verb@AttributeError@ is
-raised.  Otherwise, the type and value of the object produced is
-determined by the object.  Multiple evaluations of the same attribute
-reference may yield different objects.
-\obindex{module}
-\obindex{list}
-
-\subsection{Subscriptions}
-\index{subscription}
-
-A subscription selects an item of a sequence (string, tuple or list)
-or mapping (dictionary) object:
-\obindex{sequence}
-\obindex{mapping}
-\obindex{string}
-\obindex{tuple}
-\obindex{list}
-\obindex{dictionary}
-\indexii{sequence}{item}
-
-\begin{verbatim}
-subscription:   primary "[" condition "]"
-\end{verbatim}
-
-The primary must evaluate to an object of a sequence or mapping type.
-
-If it is a mapping, the condition must evaluate to an object whose
-value is one of the keys of the mapping, and the subscription selects
-the value in the mapping that corresponds to that key.
-
-If it is a sequence, the condition must evaluate to a plain integer.
-If this value is negative, the length of the sequence is added to it
-(so that, e.g. \verb@x[-1]@ selects the last item of \verb@x@.)
-The resulting value must be a nonnegative integer smaller than the
-number of items in the sequence, and the subscription selects the item
-whose index is that value (counting from zero).
-
-A string's items are characters.  A character is not a separate data
-type but a string of exactly one character.
-\index{character}
-\indexii{string}{item}
-
-\subsection{Slicings}
-\index{slicing}
-\index{slice}
-
-A slicing (or slice) selects a range of items in a sequence (string,
-tuple or list) object:
-\obindex{sequence}
-\obindex{string}
-\obindex{tuple}
-\obindex{list}
-
-\begin{verbatim}
-slicing:        primary "[" [condition] ":" [condition] "]"
-\end{verbatim}
-
-The primary must evaluate to a sequence object.  The lower and upper
-bound expressions, if present, must evaluate to plain integers;
-defaults are zero and the sequence's length, respectively.  If either
-bound is negative, the sequence's length is added to it.  The slicing
-now selects all items with index \var{k} such that
-\code{\var{i} <= \var{k} < \var{j}} where \var{i}
-and \var{j} are the specified lower and upper bounds.  This may be an
-empty sequence.  It is not an error if \var{i} or \var{j} lie outside the
-range of valid indexes (such items don't exist so they aren't
-selected).
-
-\subsection{Calls} \label{calls}
-\index{call}
-
-A call calls a callable object (e.g. a function) with a possibly empty
-series of arguments:\footnote{The new syntax for keyword arguments is
-not yet documented in this manual.  See chapter 12 of the Tutorial.}
-\obindex{callable}
-
-\begin{verbatim}
-call:           primary "(" [condition_list] ")"
-\end{verbatim}
-
-The primary must evaluate to a callable object (user-defined
-functions, built-in functions, methods of built-in objects, class
-objects, and methods of class instances are callable).  If it is a
-class, the argument list must be empty; otherwise, the arguments are
-evaluated.
-
-A call always returns some value, possibly \verb@None@, unless it
-raises an exception.  How this value is computed depends on the type
-of the callable object.  If it is:
-
-\begin{description}
-
-\item[a user-defined function:] the code block for the function is
-executed, passing it the argument list.  The first thing the code
-block will do is bind the formal parameters to the arguments; this is
-described in section \ref{function}.  When the code block executes a
-\verb@return@ statement, this specifies the return value of the
-function call.
-\indexii{function}{call}
-\indexiii{user-defined}{function}{call}
-\obindex{user-defined function}
-\obindex{function}
-
-\item[a built-in function or method:] the result is up to the
-interpreter; see the library reference manual for the descriptions of
-built-in functions and methods.
-\indexii{function}{call}
-\indexii{built-in function}{call}
-\indexii{method}{call}
-\indexii{built-in method}{call}
-\obindex{built-in method}
-\obindex{built-in function}
-\obindex{method}
-\obindex{function}
-
-\item[a class object:] a new instance of that class is returned.
-\obindex{class}
-\indexii{class object}{call}
-
-\item[a class instance method:] the corresponding user-defined
-function is called, with an argument list that is one longer than the
-argument list of the call: the instance becomes the first argument.
-\obindex{class instance}
-\obindex{instance}
-\indexii{instance}{call}
-\indexii{class instance}{call}
-
-\end{description}
-
-\section{Unary arithmetic operations}
-\indexiii{unary}{arithmetic}{operation}
-\indexiii{unary}{bit-wise}{operation}
-
-All unary arithmetic (and bit-wise) operations have the same priority:
-
-\begin{verbatim}
-u_expr:         primary | "-" u_expr | "+" u_expr | "~" u_expr
-\end{verbatim}
-
-The unary \verb@"-"@ (minus) operator yields the negation of its
-numeric argument.
-\index{negation}
-\index{minus}
-
-The unary \verb@"+"@ (plus) operator yields its numeric argument
-unchanged.
-\index{plus}
-
-The unary \verb@"~"@ (invert) operator yields the bit-wise inversion
-of its plain or long integer argument.  The bit-wise inversion of
-\verb@x@ is defined as \verb@-(x+1)@.
-\index{inversion}
-
-In all three cases, if the argument does not have the proper type,
-a \verb@TypeError@ exception is raised.
-\exindex{TypeError}
-
-\section{Binary arithmetic operations}
-\indexiii{binary}{arithmetic}{operation}
-
-The binary arithmetic operations have the conventional priority
-levels.  Note that some of these operations also apply to certain
-non-numeric types.  There is no ``power'' operator, so there are only
-two levels, one for multiplicative operators and one for additive
-operators:
-
-\begin{verbatim}
-m_expr:         u_expr | m_expr "*" u_expr
-              | m_expr "/" u_expr | m_expr "%" u_expr
-a_expr:         m_expr | aexpr "+" m_expr | aexpr "-" m_expr
-\end{verbatim}
-
-The \verb@"*"@ (multiplication) operator yields the product of its
-arguments.  The arguments must either both be numbers, or one argument
-must be a plain integer and the other must be a sequence.  In the
-former case, the numbers are converted to a common type and then
-multiplied together.  In the latter case, sequence repetition is
-performed; a negative repetition factor yields an empty sequence.
-\index{multiplication}
-
-The \verb@"/"@ (division) operator yields the quotient of its
-arguments.  The numeric arguments are first converted to a common
-type.  Plain or long integer division yields an integer of the same
-type; the result is that of mathematical division with the `floor'
-function applied to the result.  Division by zero raises the
-\verb@ZeroDivisionError@ exception.
-\exindex{ZeroDivisionError}
-\index{division}
-
-The \verb@"%"@ (modulo) operator yields the remainder from the
-division of the first argument by the second.  The numeric arguments
-are first converted to a common type.  A zero right argument raises
-the \verb@ZeroDivisionError@ exception.  The arguments may be floating
-point numbers, e.g. \verb@3.14 % 0.7@ equals \verb@0.34@.  The modulo
-operator always yields a result with the same sign as its second
-operand (or zero); the absolute value of the result is strictly
-smaller than the second operand.
-\index{modulo}
-
-The integer division and modulo operators are connected by the
-following identity: \verb@x == (x/y)*y + (x%y)@.  Integer division and
-modulo are also connected with the built-in function \verb@divmod()@:
-\verb@divmod(x, y) == (x/y, x%y)@.  These identities don't hold for
-floating point numbers; there a similar identity holds where
-\verb@x/y@ is replaced by \verb@floor(x/y)@).
-
-The \verb@"+"@ (addition) operator yields the sum of its arguments.
-The arguments must either both be numbers, or both sequences of the
-same type.  In the former case, the numbers are converted to a common
-type and then added together.  In the latter case, the sequences are
-concatenated.
-\index{addition}
-
-The \verb@"-"@ (subtraction) operator yields the difference of its
-arguments.  The numeric arguments are first converted to a common
-type.
-\index{subtraction}
-
-\section{Shifting operations}
-\indexii{shifting}{operation}
-
-The shifting operations have lower priority than the arithmetic
-operations:
-
-\begin{verbatim}
-shift_expr:     a_expr | shift_expr ( "<<" | ">>" ) a_expr
-\end{verbatim}
-
-These operators accept plain or long integers as arguments.  The
-arguments are converted to a common type.  They shift the first
-argument to the left or right by the number of bits given by the
-second argument.
-
-A right shift by \var{n} bits is defined as division by
-\code{pow(2,\var{n})}.  A left shift by \var{n} bits is defined as
-multiplication with \code{pow(2,\var{n})}; for plain integers there is
-no overflow check so this drops bits and flips the sign if the result
-is not less than \code{pow(2,31)} in absolute value.
-
-Negative shift counts raise a \verb@ValueError@ exception.
-\exindex{ValueError}
-
-\section{Binary bit-wise operations}
-\indexiii{binary}{bit-wise}{operation}
-
-Each of the three bitwise operations has a different priority level:
-
-\begin{verbatim}
-and_expr:       shift_expr | and_expr "&" shift_expr
-xor_expr:       and_expr | xor_expr "^" and_expr
-or_expr:       xor_expr | or_expr "|" xor_expr
-\end{verbatim}
-
-The \verb@"&"@ operator yields the bitwise AND of its arguments, which
-must be plain or long integers.  The arguments are converted to a
-common type.
-\indexii{bit-wise}{and}
-
-The \verb@"^"@ operator yields the bitwise XOR (exclusive OR) of its
-arguments, which must be plain or long integers.  The arguments are
-converted to a common type.
-\indexii{bit-wise}{xor}
-\indexii{exclusive}{or}
-
-The \verb@"|"@ operator yields the bitwise (inclusive) OR of its
-arguments, which must be plain or long integers.  The arguments are
-converted to a common type.
-\indexii{bit-wise}{or}
-\indexii{inclusive}{or}
-
-\section{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
-\verb@a < b < c@ have the interpretation that is conventional in
-mathematics:
-\index{C}
-
-\begin{verbatim}
-comparison:     or_expr (comp_operator or_expr)*
-comp_operator:  "<"|">"|"=="|">="|"<="|"<>"|"!="|"is" ["not"]|["not"] "in"
-\end{verbatim}
-
-Comparisons yield integer values: 1 for true, 0 for false.
-
-Comparisons can be chained arbitrarily, e.g. \code{x < y <= z} is
-equivalent to \code{x < y and y <= z}, except that \code{y} is
-evaluated only once (but in both cases \code{z} is not evaluated at all
-when \code{x < y} is found to be false).
-\indexii{chaining}{comparisons}
-
-Formally, if \var{a}, \var{b}, \var{c}, \ldots, \var{y}, \var{z} are
-expressions and \var{opa}, \var{opb}, \ldots, \var{opy} are comparison
-operators, then \var{a opa b opb c} \ldots \var{y opy z} is equivalent
-to \var{a opa b} \code{and} \var{b opb c} \code{and} \ldots \code{and}
-\var{y opy z}, except that each expression is evaluated at most once.
-
-Note that \var{a opa b opb c} doesn't imply any kind of comparison
-between \var{a} and \var{c}, so that e.g.\ \code{x < y > z} is
-perfectly legal (though perhaps not pretty).
-
-The forms \verb@<>@ and \verb@!=@ are equivalent; for consistency with
-C, \verb@!=@ is preferred; where \verb@!=@ is mentioned below
-\verb@<>@ is also implied.
-
-The operators {\tt "<", ">", "==", ">=", "<="}, and {\tt "!="} compare
-the values of two objects.  The objects needn't have the same type.
-If both are numbers, they are coverted to a common type.  Otherwise,
-objects of different types {\em always} compare unequal, and are
-ordered consistently but arbitrarily.
-
-(This unusual definition of comparison is done to simplify the
-definition of operations like sorting and the \verb@in@ and
-\verb@not@ \verb@in@ operators.)
-
-Comparison of objects of the same type depends on the type:
-
-\begin{itemize}
-
-\item
-Numbers are compared arithmetically.
-
-\item
-Strings are compared lexicographically using the numeric equivalents
-(the result of the built-in function \verb@ord@) of their characters.
-
-\item
-Tuples and lists are compared lexicographically using comparison of
-corresponding items.
-
-\item
-Mappings (dictionaries) are compared through lexicographic
-comparison of their sorted (key, value) lists.%
-\footnote{This is expensive since it requires sorting the keys first,
-but about the only sensible definition.  An earlier version of Python
-compared dictionaries by identity only, but this caused surprises
-because people expected to be able to test a dictionary for emptiness
-by comparing it to {\tt \{\}}.}
-
-\item
-Most other types compare unequal unless they are the same object;
-the choice whether one object is considered smaller or larger than
-another one is made arbitrarily but consistently within one
-execution of a program.
-
-\end{itemize}
-
-The operators \verb@in@ and \verb@not in@ test for sequence
-membership: if \var{y} is a sequence, \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}]}.
-\code{\var{x} not in \var{y}} yields the inverse truth value.  The
-exception \verb@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 one.%
-\footnote{The latter restriction is sometimes a nuisance.}
-\opindex{in}
-\opindex{not in}
-\indexii{membership}{test}
-\obindex{sequence}
-
-The operators \verb@is@ and \verb@is not@ test for object identity:
-\var{x} \code{is} \var{y} is true if and only if \var{x} and \var{y}
-are the same object.  \var{x} \code{is not} \var{y} yields the inverse
-truth value.
-\opindex{is}
-\opindex{is not}
-\indexii{identity}{test}
-
-\section{Boolean operations} \label{Booleans}
-\indexii{Boolean}{operation}
-
-Boolean operations have the lowest priority of all Python operations:
-
-\begin{verbatim}
-condition:      or_test | lambda_form
-or_test:        and_test | or_test "or" and_test
-and_test:       not_test | and_test "and" not_test
-not_test:       comparison | "not" not_test
-lambda_form:	"lambda" [parameter_list]: condition
-\end{verbatim}
-
-In the context of Boolean operations, and also when conditions are
-used by control flow statements, the following values are interpreted
-as false: \verb@None@, numeric zero of all types, empty sequences
-(strings, tuples and lists), and empty mappings (dictionaries).  All
-other values are interpreted as true.
-
-The operator \verb@not@ yields 1 if its argument is false, 0 otherwise.
-\opindex{not}
-
-The condition \var{x} \verb@and@ \var{y} first evaluates \var{x}; if
-\var{x} is false, its value is returned; otherwise, \var{y} is
-evaluated and the resulting value is returned.
-\opindex{and}
-
-The condition \var{x} \verb@or@ \var{y} first evaluates \var{x}; if
-\var{x} is true, its value is returned; otherwise, \var{y} is
-evaluated and the resulting value is returned.
-\opindex{or}
-
-(Note that \verb@and@ and \verb@or@ do not restrict the value and type
-they return to 0 and 1, but rather return the last evaluated argument.
-This is sometimes useful, e.g. if \verb@s@ is a string that should be
-replaced by a default value if it is empty, the expression
-\verb@s or 'foo'@ yields the desired value.  Because \verb@not@ has to
-invent a value anyway, it does not bother to return a value of the
-same type as its argument, so e.g. \verb@not 'foo'@ yields \verb@0@,
-not \verb@''@.)
-
-Lambda forms (lambda expressions) have the same syntactic position as
-conditions.  They are a shorthand to create anonymous functions; the
-expression {\em {\tt lambda} arguments{\tt :} condition}
-yields a function object that behaves virtually identical to one
-defined with
-{\em {\tt def} name {\tt (}arguments{\tt ): return} condition}.
-See section \ref{function} for the syntax of
-parameter lists.  Note that functions created with lambda forms cannot
-contain statements.
-\label{lambda}
-\indexii{lambda}{expression}
-\indexii{lambda}{form}
-\indexii{anonmymous}{function}
-
-\section{Expression lists and condition lists}
-\indexii{expression}{list}
-\indexii{condition}{list}
-
-\begin{verbatim}
-expression_list:      or_expr ("," or_expr)* [","]
-condintion_list:      condition ("," condition)* [","]
-\end{verbatim}
-
-The only difference between expression lists and condition lists is
-the lowest priority of operators that can be used in them without
-being enclosed in parentheses; condition lists allow all operators,
-while expression lists don't allow comparisons and Boolean operators
-(they do allow bitwise and shift operators though).
-
-Expression lists are used in expression statements and assignments;
-condition lists are used everywhere else where a list of
-comma-separated values is required.
-
-An expression (condition) list containing at least one comma yields a
-tuple.  The length of the tuple is the number of expressions
-(conditions) in the list.  The expressions (conditions) are evaluated
-from left to right.  (Condition lists are used syntactically is a few
-places where no tuple is constructed but a list of values is needed
-nevertheless.)
-\obindex{tuple}
-
-The trailing comma is required only to create a single tuple (a.k.a. a
-{\em singleton}); it is optional in all other cases.  A single
-expression (condition) without a trailing comma doesn't create a
-tuple, but rather yields the value of that expression (condition).
-\indexii{trailing}{comma}
-
-(To create an empty tuple, use an empty pair of parentheses:
-\verb@()@.)
-
-\section{Summary}
-
-The following table summarizes the operator precedences in Python,
-from lowest precedence (least binding) to highest precedence (most
-binding).  Operators in the same box have the same precedence.  Unless
-the syntax is explicitly given, operators are binary.  Operators in
-the same box group left to right (except for comparisons, which
-chain from left to right --- see above).
-
-\begin{center}
-\begin{tabular}{|c|c|}
-\hline
-\code{or} & Boolean OR \\
-\hline
-\code{and} & Boolean AND \\
-\hline
-\code{not} \var{x} & Boolean NOT \\
-\hline
-\code{in}, \code{not} \code{in} & Membership tests \\
-\code{is}, \code{is} \code{not} & Identity tests \\
-\code{<}, \code{<=}, \code{>}, \code{>=}, \code{<>}, \code{!=}, \code{=} &
-	Comparisons \\
-\hline
-\code{|} & Bitwise OR \\
-\hline
-\code{\^} & Bitwise XOR \\
-\hline
-\code{\&} & Bitwise AND \\
-\hline
-\code{<<}, \code{>>} & Shifts \\
-\hline
-\code{+}, \code{-} & Addition and subtraction \\
-\hline
-\code{*}, \code{/}, \code{\%} & Multiplication, division, remainder \\
-\hline
-\code{+\var{x}}, \code{-\var{x}} & Positive, negative \\
-\code{\~\var{x}} & Bitwise not \\
-\hline
-\code{\var{x}.\var{attribute}} & Attribute reference \\
-\code{\var{x}[\var{index}]} &  Subscription \\
-\code{\var{x}[\var{index}:\var{index}]} &  Slicing \\
-\code{\var{f}(\var{arguments}...)} & Function call \\
-\hline
-\code{(\var{expressions}\ldots)} & Binding or tuple display \\
-\code{[\var{expressions}\ldots]} & List display \\
-\code{\{\var{key}:\var{datum}\ldots\}} & Dictionary display \\
-\code{`\var{expression}\ldots`} & String conversion \\
-\hline
-\end{tabular}
-\end{center}