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| -rw-r--r-- | Doc/ref/ref6.tex | 137 | ||||
| -rw-r--r-- | Doc/ref/ref7.tex | 132 | ||||
| -rw-r--r-- | Doc/ref/ref8.tex | 16 | ||||
| -rw-r--r-- | Doc/ref6.tex | 137 | ||||
| -rw-r--r-- | Doc/ref7.tex | 132 | ||||
| -rw-r--r-- | Doc/ref8.tex | 16 |
6 files changed, 308 insertions, 262 deletions
diff --git a/Doc/ref/ref6.tex b/Doc/ref/ref6.tex index 086d49b..b1d4572 100644 --- a/Doc/ref/ref6.tex +++ b/Doc/ref/ref6.tex @@ -27,14 +27,14 @@ simple_stmt: expression_stmt Expression statements are used (mostly interactively) to compute and write a value, or (usually) to call a procedure (a function that returns no meaningful result; in Python, procedures return the value -\verb\None\): +\verb@None@): \begin{verbatim} expression_stmt: expression_list \end{verbatim} An expression statement evaluates the expression list (which may be a -single expression). If the value is not \verb\None\, it is converted +single expression). If the value is not \verb@None@, it is converted to a string using the rules for string conversions (expressions in reverse quotes), and the resulting string is written to standard output (see section \ref{print}) on a line by itself. @@ -45,9 +45,9 @@ output (see section \ref{print}) on a line by itself. \indexii{standard}{output} \indexii{writing}{values} -(The exception for \verb\None\ is made so that procedure calls, which +(The exception for \verb@None@ is made so that procedure calls, which are syntactically equivalent to expressions, do not cause any output. -A tuple with only \verb\None\ items is written normally.) +A tuple with only \verb@None@ items is written normally.) \indexii{procedure}{call} \section{Assignment statements} @@ -114,7 +114,7 @@ If the target is an identifier (name): \begin{itemize} \item -If the name does not occur in a \verb\global\ statement in the current +If the name does not occur in a \verb@global@ statement in the current code block: the name is bound to the object in the current local name space. \stindex{global} @@ -140,10 +140,10 @@ the corresponding targets. \item If the target is an attribute reference: The primary expression in the reference is evaluated. It should yield an object with assignable -attributes; if this is not the case, \verb\TypeError\ is raised. That +attributes; if this is not the case, \verb@TypeError@ is raised. That object is then asked to assign the assigned object to the given attribute; if it cannot perform the assignment, it raises an exception -(usually but not necessarily \verb\AttributeError\). +(usually but not necessarily \verb@AttributeError@). \indexii{attribute}{assignment} \item @@ -159,7 +159,7 @@ must yield a plain integer. If it is negative, the sequence's length is added to it. The resulting value must be a nonnegative integer less than the sequence's length, and the sequence is asked to assign the assigned object to its item with that index. If the index is out -of range, \verb\IndexError\ is raised (assignment to a subscripted +of range, \verb@IndexError@ is raised (assignment to a subscripted sequence cannot add new items to a list). \obindex{sequence} \obindex{list} @@ -175,16 +175,17 @@ key with the same value existed). \item If the target is a slicing: The primary expression in the reference is -evaluated. It should yield a mutable sequence (list) object. The +evaluated. It should yield a mutable sequence object (e.g. a list). The assigned object should be a sequence object of the same type. Next, the lower and upper bound expressions are evaluated, insofar they are present; defaults are zero and the sequence's length. The bounds should evaluate to (small) integers. If either bound is negative, the sequence's length is added to it. The resulting bounds are clipped to lie between zero and the sequence's length, inclusive. Finally, the -sequence object is asked to replace the items indicated by the slice -with the items of the assigned sequence. This may change the -sequence's length, if it allows it. +sequence object is asked to replace the slice with the items of the +assigned sequence. The length of the slice may be different from the +length of the assigned sequence, thus changing the length of the +target sequence, if the object allows it. \indexii{slicing}{assignment} \end{itemize} @@ -201,7 +202,7 @@ messages.) pass_stmt: "pass" \end{verbatim} -\verb\pass\ is a null operation --- when it is executed, nothing +\verb@pass@ is a null operation --- when it is executed, nothing happens. It is useful as a placeholder when a statement is required syntactically, but no code needs to be executed, for example: \indexii{null}{operation} @@ -230,7 +231,7 @@ to right. Deletion of a name removes the binding of that name (which must exist) from the local or global name space, depending on whether the name -occurs in a \verb\global\ statement in the same code block. +occurs in a \verb@global@ statement in the same code block. \stindex{global} \indexii{unbinding}{name} @@ -247,7 +248,7 @@ right type (but even this is determined by the sliced object). print_stmt: "print" [ condition ("," condition)* [","] ] \end{verbatim} -\verb\print\ evaluates each condition in turn and writes the resulting +\verb@print@ evaluates each condition in turn and writes the resulting object to standard output (see below). If an object is not a string, it is first converted to a string using the rules for string conversions. The (resulting or original) string is then written. A @@ -256,21 +257,21 @@ the output system believes it is positioned at the beginning of a line. This is the case: (1) when no characters have yet been written to standard output; or (2) when the last character written to standard output is \verb/\n/; or (3) when the last write operation on standard -output was not a \verb\print\ statement. (In some cases it may be +output was not a \verb@print@ statement. (In some cases it may be functional to write an empty string to standard output for this reason.) \index{output} \indexii{writing}{values} -A \verb/"\n"/ character is written at the end, unless the \verb\print\ +A \verb/"\n"/ character is written at the end, unless the \verb@print@ statement ends with a comma. This is the only action if the statement -contains just the keyword \verb\print\. +contains just the keyword \verb@print@. \indexii{trailing}{comma} \indexii{newline}{suppression} -Standard output is defined as the file object named \verb\stdout\ -in the built-in module \verb\sys\. If no such object exists, -or if it is not a writable file, a \verb\RuntimeError\ exception is raised. +Standard output is defined as the file object named \verb@stdout@ +in the built-in module \verb@sys@. If no such object exists, +or if it is not a writable file, a \verb@RuntimeError@ exception is raised. (The original implementation attempts to write to the system's original standard output instead, but this is not safe, and should be fixed.) \indexii{standard}{output} @@ -285,19 +286,19 @@ standard output instead, but this is not safe, and should be fixed.) return_stmt: "return" [condition_list] \end{verbatim} -\verb\return\ may only occur syntactically nested in a function +\verb@return@ may only occur syntactically nested in a function definition, not within a nested class definition. \indexii{function}{definition} \indexii{class}{definition} -If a condition list is present, it is evaluated, else \verb\None\ +If a condition list is present, it is evaluated, else \verb@None@ is substituted. -\verb\return\ leaves the current function call with the condition -list (or \verb\None\) as return value. +\verb@return@ leaves the current function call with the condition +list (or \verb@None@) as return value. -When \verb\return\ passes control out of a \verb\try\ statement -with a \verb\finally\ clause, that finally clause is executed +When \verb@return@ passes control out of a \verb@try@ statement +with a \verb@finally@ clause, that finally clause is executed before really leaving the function. \kwindex{finally} @@ -308,14 +309,14 @@ before really leaving the function. raise_stmt: "raise" condition ["," condition] \end{verbatim} -\verb\raise\ evaluates its first condition, which must yield +\verb@raise@ evaluates its first condition, which must yield a string object. If there is a second condition, this is evaluated, -else \verb\None\ is substituted. +else \verb@None@ is substituted. \index{exception} \indexii{raising}{exception} It then raises the exception identified by the first object, -with the second one (or \verb\None\) as its parameter. +with the second one (or \verb@None@) as its parameter. \section{The {\tt break} statement} \stindex{break} @@ -324,22 +325,23 @@ with the second one (or \verb\None\) as its parameter. break_stmt: "break" \end{verbatim} -\verb\break\ may only occur syntactically nested in a \verb\for\ -or \verb\while\ loop, not nested in a function or class definition. +\verb@break@ may only occur syntactically nested in a \verb@for@ +or \verb@while@ loop, but not nested in a function or class definition +within that loop. \stindex{for} \stindex{while} \indexii{loop}{statement} -It terminates the neares enclosing loop, skipping the optional -\verb\else\ clause if the loop has one. +It terminates the nearest enclosing loop, skipping the optional +\verb@else@ clause if the loop has one. \kwindex{else} -If a \verb\for\ loop is terminated by \verb\break\, the loop control +If a \verb@for@ loop is terminated by \verb@break@, the loop control target keeps its current value. \indexii{loop control}{target} -When \verb\break\ passes control out of a \verb\try\ statement -with a \verb\finally\ clause, that finally clause is executed +When \verb@break@ passes control out of a \verb@try@ statement +with a \verb@finally@ clause, that finally clause is executed before really leaving the loop. \kwindex{finally} @@ -350,11 +352,10 @@ before really leaving the loop. continue_stmt: "continue" \end{verbatim} -\verb\continue\ may only occur syntactically nested in a \verb\for\ or -\verb\while\ loop, not nested in a function or class definition, and -not nested in the \verb\try\ clause of a \verb\try\ statement with a -\verb\finally\ clause (it may occur nested in a \verb\except\ or -\verb\finally\ clause of a \verb\try\ statement though). +\verb@continue@ may only occur syntactically nested in a \verb@for@ or +\verb@while@ loop, but not nested in a function or class definition or +\verb@try@ statement within that loop.\footnote{Except that it may +currently occur within an \verb@except@ clause.} \stindex{for} \stindex{while} \indexii{loop}{statement} @@ -373,9 +374,9 @@ import_stmt: "import" identifier ("," identifier)* Import statements are executed in two steps: (1) find a module, and initialize it if necessary; (2) define a name or names in the local -name space (of the scope where the \verb\import\ statement occurs). -The first form (without \verb\from\) repeats these steps for each -identifier in the list, the \verb\from\ form performs them once, with +name space (of the scope where the \verb@import@ statement occurs). +The first form (without \verb@from@) repeats these steps for each +identifier in the list, the \verb@from@ form performs them once, with the first identifier specifying the module name. \indexii{importing}{module} \indexii{name}{binding} @@ -383,15 +384,15 @@ the first identifier specifying the module name. The system maintains a table of modules that have been initialized, indexed by module name. (The current implementation makes this table -accessible as \verb\sys.modules\.) When a module name is found in +accessible as \verb@sys.modules@.) When a module name is found in this table, step (1) is finished. If not, a search for a module definition is started. This first looks for a built-in module definition, and if no built-in module if the given name is found, it searches a user-specified list of directories for a file whose name is -the module name with extension \verb\".py"\. (The current -implementation uses the list of strings \verb\sys.path\ as the search +the module name with extension \verb@".py"@. (The current +implementation uses the list of strings \verb@sys.path@ as the search path; it is initialized from the shell environment variable -\verb\$PYTHONPATH\, with an installation-dependent default.) +\verb@$PYTHONPATH@, with an installation-dependent default.) \ttindex{modules} \ttindex{sys.modules} \indexii{module}{name} @@ -404,9 +405,9 @@ path; it is initialized from the shell environment variable If a built-in module is found, its built-in initialization code is executed and step (1) is finished. If no matching file is found, -\verb\ImportError\ is raised. If a file is found, it is parsed, +\verb@ImportError@ is raised. If a file is found, it is parsed, yielding an executable code block. If a syntax error occurs, -\verb\SyntaxError\ is raised. Otherwise, an empty module of the given +\verb@SyntaxError@ is raised. Otherwise, an empty module of the given name is created and inserted in the module table, and then the code block is executed in the context of this module. Exceptions during this execution terminate step (1). @@ -418,23 +419,23 @@ this execution terminate step (1). When step (1) finishes without raising an exception, step (2) can begin. -The first form of \verb\import\ statement binds the module name in the +The first form of \verb@import@ statement binds the module name in the local name space to the module object, and then goes on to import the -next identifier, if any. The \verb\from\ from does not bind the +next identifier, if any. The \verb@from@ from does not bind the module name: it goes through the list of identifiers, looks each one of them up in the module found in step (1), and binds the name in the local name space to the object thus found. If a name is not found, -\verb\ImportError\ is raised. If the list of identifiers is replaced -by a star (\verb\*\), all names defined in the module are bound, -except those beginning with an underscore(\verb\_\). +\verb@ImportError@ is raised. If the list of identifiers is replaced +by a star (\verb@*@), all names defined in the module are bound, +except those beginning with an underscore(\verb@_@). \indexii{name}{binding} \exindex{ImportError} -Names bound by import statements may not occur in \verb\global\ +Names bound by import statements may not occur in \verb@global@ statements in the same scope. \stindex{global} -The \verb\from\ form with \verb\*\ may only occur in a module scope. +The \verb@from@ form with \verb@*@ may only occur in a module scope. \kwindex{from} \ttindex{from ... import *} @@ -450,19 +451,19 @@ program.) global_stmt: "global" identifier ("," identifier)* \end{verbatim} -The \verb\global\ statement is a declaration which holds for the +The \verb@global@ statement is a declaration which holds for the entire current scope. It means that the listed identifiers are to be interpreted as globals. While {\em using} global names is automatic if they are not defined in the local scope, {\em assigning} to global -names would be impossible without \verb\global\. +names would be impossible without \verb@global@. \indexiii{global}{name}{binding} -Names listed in a \verb\global\ statement must not be used in the same -scope before that \verb\global\ statement is executed. +Names listed in a \verb@global@ statement must not be used in the same +scope before that \verb@global@ statement is executed. -Names listed in a \verb\global\ statement must not be defined as formal -parameters or in a \verb\for\ loop control target, \verb\class\ -definition, function definition, or \verb\import\ statement. +Names listed in a \verb@global@ statement must not be defined as formal +parameters or in a \verb@for@ loop control target, \verb@class@ +definition, function definition, or \verb@import@ statement. (The current implementation does not enforce the latter two restrictions, but programs should not abuse this freedom, as future @@ -478,7 +479,7 @@ access_stmt: "access" ... This statement will be used in the future to control access to instance and class variables. Currently its syntax and effects are -undefined; however the keyword \verb\access\ is a reserved word for +undefined; however the keyword \verb@access@ is a reserved word for the parser. \section{The {\tt exec} statement} \label{exec} @@ -496,12 +497,12 @@ occurs). If it is an open file, the file is parsed until EOF and executed. If it is a code object, it is simply executed. In all cases, if the optional parts are omitted, the code is executed -in the current scope. If only the first expression after \verb\in\ is +in the current scope. If only the first expression after \verb@in@ is specified, it should be a dictionary, which will be used for both the global and the local variables. If two expressions are given, both must be dictionaries and they are used for the global and local variables, respectively. Note: dynamic evaluation of expressions is supported by the built-in -function \verb\eval\. +function \verb@eval@. diff --git a/Doc/ref/ref7.tex b/Doc/ref/ref7.tex index 670eec0..b8babfb9 100644 --- a/Doc/ref/ref7.tex +++ b/Doc/ref/ref7.tex @@ -6,8 +6,8 @@ or control the execution of those other statements in some way. In general, compound statements span multiple lines, although in simple incarnations a whole compound statement may be contained in one line. -The \verb\if\, \verb\while\ and \verb\for\ statements implement -traditional control flow constructs. \verb\try\ specifies exception +The \verb@if@, \verb@while@ and \verb@for@ statements implement +traditional control flow constructs. \verb@try@ specifies exception handlers and/or cleanup code for a group of statements. Function and class definitions are also syntactically compound statements. @@ -21,7 +21,7 @@ statements on the same line as the header, following the header's colon, or it can be one or more indented statements on subsequent lines. Only the latter form of suite can contain nested compound statements; the following is illegal, mostly because it wouldn't be -clear to which \verb\if\ clause a following \verb\else\ clause would +clear to which \verb@if@ clause a following \verb@else@ clause would belong: \index{clause} \index{suite} @@ -32,7 +32,7 @@ if test1: if test2: print x Also note that the semicolon binds tighter than the colon in this context, so that in the following example, either all or none of the -\verb\print\ statements are executed: +\verb@print@ statements are executed: \begin{verbatim} if x < y < z: print x; print y; print z @@ -48,15 +48,15 @@ statement: stmt_list NEWLINE | compound_stmt stmt_list: simple_stmt (";" simple_stmt)* [";"] \end{verbatim} -Note that statements always end in a \verb\NEWLINE\ possibly followed -by a \verb\DEDENT\. +Note that statements always end in a \verb@NEWLINE@ possibly followed +by a \verb@DEDENT@. \index{NEWLINE token} \index{DEDENT token} Also note that optional continuation clauses always begin with a keyword that cannot start a statement, thus there are no ambiguities -(the `dangling \verb\else\' problem is solved in Python by requiring -nested \verb\if\ statements to be indented). +(the `dangling \verb@else@' problem is solved in Python by requiring +nested \verb@if@ statements to be indented). \indexii{dangling}{else} The formatting of the grammar rules in the following sections places @@ -65,7 +65,7 @@ each clause on a separate line for clarity. \section{The {\tt if} statement} \stindex{if} -The \verb\if\ statement is used for conditional execution: +The \verb@if@ statement is used for conditional execution: \begin{verbatim} if_stmt: "if" condition ":" suite @@ -76,8 +76,8 @@ if_stmt: "if" condition ":" suite It selects exactly one of the suites by evaluating the conditions one by one until one is found to be true (see section \ref{Booleans} for the definition of true and false); then that suite is executed (and no -other part of the \verb\if\ statement is executed or evaluated). If -all conditions are false, the suite of the \verb\else\ clause, if +other part of the \verb@if@ statement is executed or evaluated). If +all conditions are false, the suite of the \verb@else@ clause, if present, is executed. \kwindex{elif} \kwindex{else} @@ -86,7 +86,7 @@ present, is executed. \stindex{while} \indexii{loop}{statement} -The \verb\while\ statement is used for repeated execution as long as a +The \verb@while@ statement is used for repeated execution as long as a condition is true: \begin{verbatim} @@ -96,13 +96,13 @@ while_stmt: "while" condition ":" suite This repeatedly tests the condition and, if it is true, executes the first suite; if the condition is false (which may be the first time it -is tested) the suite of the \verb\else\ clause, if present, is +is tested) the suite of the \verb@else@ clause, if present, is executed and the loop terminates. \kwindex{else} -A \verb\break\ statement executed in the first suite terminates the -loop without executing the \verb\else\ clause's suite. A -\verb\continue\ statement executed in the first suite skips the rest +A \verb@break@ statement executed in the first suite terminates the +loop without executing the \verb@else@ clause's suite. A +\verb@continue@ statement executed in the first suite skips the rest of the suite and goes back to testing the condition. \stindex{break} \stindex{continue} @@ -111,7 +111,7 @@ of the suite and goes back to testing the condition. \stindex{for} \indexii{loop}{statement} -The \verb\for\ statement is used to iterate over the elements of a +The \verb@for@ statement is used to iterate over the elements of a sequence (string, tuple or list): \obindex{sequence} @@ -125,16 +125,16 @@ suite is then executed once for each item in the sequence, in the order of ascending indices. Each item in turn is assigned to the target list using the standard rules for assignments, and then the suite is executed. When the items are exhausted (which is immediately -when the sequence is empty), the suite in the \verb\else\ clause, if +when the sequence is empty), the suite in the \verb@else@ clause, if present, is executed, and the loop terminates. \kwindex{in} \kwindex{else} \indexii{target}{list} -A \verb\break\ statement executed in the first suite terminates the -loop without executing the \verb\else\ clause's suite. A -\verb\continue\ statement executed in the first suite skips the rest -of the suite and continues with the next item, or with the \verb\else\ +A \verb@break@ statement executed in the first suite terminates the +loop without executing the \verb@else@ clause's suite. A +\verb@continue@ statement executed in the first suite skips the rest +of the suite and continues with the next item, or with the \verb@else@ clause if there was no next item. \stindex{break} \stindex{continue} @@ -146,9 +146,10 @@ The target list is not deleted when the loop is finished, but if the sequence is empty, it will not have been assigned to at all by the loop. -Hint: the built-in function \verb\range()\ returns a sequence of -integers suitable to emulate the effect of Pascal's \verb\for i := a -to b do\; e.g. \verb\range(3)\ returns the list \verb\[0, 1, 2]\. +Hint: the built-in function \verb@range()@ returns a sequence of +integers suitable to emulate the effect of Pascal's +\verb@for i := a to b do@; +e.g. \verb@range(3)@ returns the list \verb@[0, 1, 2]@. \bifuncindex{range} \index{Pascal} @@ -175,24 +176,25 @@ for x in a[:]: \section{The {\tt try} statement} \label{try} \stindex{try} -The \verb\try\ statement specifies exception handlers and/or cleanup +The \verb@try@ statement specifies exception handlers and/or cleanup code for a group of statements: \begin{verbatim} try_stmt: try_exc_stmt | try_fin_stmt try_exc_stmt: "try" ":" suite ("except" [condition ["," target]] ":" suite)+ + ["else" ":" suite] try_fin_stmt: "try" ":" suite "finally" ":" suite \end{verbatim} -There are two forms of \verb\try\ statement: \verb\try...except\ and -\verb\try...finally\. These forms cannot be mixed. +There are two forms of \verb@try@ statement: \verb@try...except@ and +\verb@try...finally@. These forms cannot be mixed. -The \verb\try...except\ form specifies one or more exception handlers -(the \verb\except\ clauses). When no exception occurs in the -\verb\try\ clause, no exception handler is executed. When an -exception occurs in the \verb\try\ suite, a search for an exception +The \verb@try...except@ form specifies one or more exception handlers +(the \verb@except@ clauses). When no exception occurs in the +\verb@try@ clause, no exception handler is executed. When an +exception occurs in the \verb@try@ suite, a search for an exception handler is started. This inspects the except clauses in turn until one is found that matches the exception. A condition-less except clause, if present, must be last; it matches any exception. For an @@ -211,7 +213,7 @@ handler continues in the surrounding code and on the invocation stack. If the evaluation of a condition in the header of an except clause raises an exception, the original search for a handler is cancelled and a search starts for the new exception in the surrounding code and -on the call stack (it is treated as if the entire \verb\try\ statement +on the call stack (it is treated as if the entire \verb@try@ statement raised the exception). When a matching except clause is found, the exception's parameter is @@ -223,10 +225,10 @@ exception, and the exception occurs in the try clause of the inner handler, the outer handler will not handle the exception.) Before an except clause's suite is executed, details about the -exception are assigned to three variables in the \verb\sys\ module: -\verb\sys.exc_type\ receives the object identifying the exception; -\verb\sys.exc_value\ receives the exception's parameter; -\verb\sys.exc_traceback\ receives a traceback object (see section +exception are assigned to three variables in the \verb@sys@ module: +\verb@sys.exc_type@ receives the object identifying the exception; +\verb@sys.exc_value@ receives the exception's parameter; +\verb@sys.exc_traceback@ receives a traceback object (see section \ref{traceback}) identifying the point in the program where the exception occurred. \bimodindex{sys} @@ -235,20 +237,25 @@ exception occurred. \ttindex{exc_traceback} \obindex{traceback} -The \verb\try...finally\ form specifies a `cleanup' handler. The -\verb\try\ clause is executed. When no exception occurs, the -\verb\finally\ clause is executed. When an exception occurs in the -\verb\try\ clause, the exception is temporarily saved, the -\verb\finally\ clause is executed, and then the saved exception is -re-raised. If the \verb\finally\ clause raises another exception or -executes a \verb\return\, \verb\break\ or \verb\continue\ statement, +The optional \verb@else@ clause is executed when no exception occurs +in the \verb@try@ clause. Exceptions in the \verb@else@ clause are +not handled by the preceding \verb@except@ clauses. +\kwindex{else} + +The \verb@try...finally@ form specifies a `cleanup' handler. The +\verb@try@ clause is executed. When no exception occurs, the +\verb@finally@ clause is executed. When an exception occurs in the +\verb@try@ clause, the exception is temporarily saved, the +\verb@finally@ clause is executed, and then the saved exception is +re-raised. If the \verb@finally@ clause raises another exception or +executes a \verb@return@, \verb@break@ or \verb@continue@ statement, the saved exception is lost. \kwindex{finally} -When a \verb\return\ or \verb\break\ statement is executed in the -\verb\try\ suite of a \verb\try...finally\ statement, the -\verb\finally\ clause is also executed `on the way out'. A -\verb\continue\ statement is illegal in the \verb\try\ clause. (The +When a \verb@return@ or \verb@break@ statement is executed in the +\verb@try@ suite of a \verb@try...finally@ statement, the +\verb@finally@ clause is also executed `on the way out'. A +\verb@continue@ statement is illegal in the \verb@try@ clause. (The reason is a problem with the current implementation --- this restriction may be lifted in the future). \stindex{return} @@ -265,7 +272,8 @@ section \ref{types}): \begin{verbatim} funcdef: "def" funcname "(" [parameter_list] ")" ":" suite -parameter_list: (parameter ",")* ("*" identifier | parameter [","]) +parameter_list: (defparameter ",")* ("*" identifier | defparameter [","]) +defparameter: parameter ["=" condition] sublist: parameter ("," parameter)* [","] parameter: identifier | "(" sublist ")" funcname: identifier @@ -282,8 +290,21 @@ as the global name space to be used when the function is called. The function definition does not execute the function body; this gets executed only when the function is called. +When one or more top-level parameters have the form {\em parameter = +condition}, the function is said to have ``default parameter values''. +Default parameter values are evaluated when the function definition is +executed. For a parameter with a default value, the correponding +argument may be omitted from a call, in which case the parameter's +default value is substituted. If a parameter has a default value, all +following parameters must also have a default value --- this is a +syntactic restriction that is not expressed by the grammar.% +\footnote{Currently this is not checked; instead, +\verb@def f(a=1,b)@ is interpreted as \verb@def f(a=1,b=None)@.} +\indexiii{default}{parameter}{value} + Function call semantics are described in section \ref{calls}. When a -user-defined function is called, the arguments (a.k.a. actual +user-defined function is called, first missing arguments for which a +default value exists are supplied; then the arguments (a.k.a. actual parameters) are bound to the (formal) parameters, as follows: \indexii{function}{call} \indexiii{user-defined}{function}{call} @@ -292,10 +313,6 @@ parameters) are bound to the (formal) parameters, as follows: \indexii{parameter}{formal} \indexii{parameter}{actual} -It is also possible to create anonymous functions (functions not bound -to a name), for immediate use in expressions. This uses lambda forms, -described in section \ref{lambda}. - \begin{itemize} \item @@ -320,7 +337,7 @@ Call this number {\em N}. The first {\em N} arguments are assigned to the corresponding formal parameters in the way descibed above. A tuple containing the remaining arguments, if any, is then assigned to the identifier following the star. This variable will always be a -tuple: if there are no extra arguments, its value is \verb\()\, if +tuple: if there are no extra arguments, its value is \verb@()@, if there is just one extra argument, it is a singleton tuple. \indexii{variable length}{parameter list} @@ -335,6 +352,11 @@ variable length parameter lists are a sufficiently accepted practice in most programming languages that a compromise has been worked out. (And anyway, assignment has no equivalent for empty argument lists.) +It is also possible to create anonymous functions (functions not bound +to a name), for immediate use in expressions. This uses lambda forms, +described in section \ref{lambda}. +\indexii{lambda}{form} + \section{Class definitions} \label{class} \indexii{class}{definition} diff --git a/Doc/ref/ref8.tex b/Doc/ref/ref8.tex index aeb65bf..1ae61ed 100644 --- a/Doc/ref/ref8.tex +++ b/Doc/ref/ref8.tex @@ -13,9 +13,9 @@ While a language specification need not prescribe how the language interpreter is invoked, it is useful to have a notion of a complete Python program. A complete Python program is executed in a minimally initialized environment: all built-in and standard modules are -available, but none have been initialized, except for \verb\sys\ -(various system services), \verb\__builtin__\ (built-in functions, -exceptions and \verb\None\) and \verb\__main__\. The latter is used +available, but none have been initialized, except for \verb@sys@ +(various system services), \verb@__builtin__@ (built-in functions, +exceptions and \verb@None@) and \verb@__main__@. The latter is used to provide the local and global name space for execution of the complete program. \bimodindex{sys} @@ -29,7 +29,7 @@ The interpreter may also be invoked in interactive mode; in this case, it does not read and execute a complete program but reads and executes one statement (possibly compound) at a time. The initial environment is identical to that of a complete program; each statement is executed -in the name space of \verb\__main__\. +in the name space of \verb@__main__@. \index{interactive mode} Under {\UNIX}, a complete program can be passed to the interpreter in @@ -58,7 +58,7 @@ This syntax is used in the following situations: \item when parsing a module; -\item when parsing a string passed to the \verb\exec\ statement; +\item when parsing a string passed to the \verb@exec@ statement; \end{itemize} @@ -80,14 +80,14 @@ end of the input. There are two forms of expression input. Both ignore leading whitespace. -The string argument to \verb\eval()\ must have the following form: +The string argument to \verb@eval()@ must have the following form: \bifuncindex{eval} \begin{verbatim} eval_input: condition_list NEWLINE* \end{verbatim} -The input line read by \verb\input()\ must have the following form: +The input line read by \verb@input()@ must have the following form: \bifuncindex{input} \begin{verbatim} @@ -95,7 +95,7 @@ input_input: condition_list NEWLINE \end{verbatim} Note: to read `raw' input line without interpretation, you can use the -built-in function \verb\raw_input()\ or the \verb\readline()\ method +built-in function \verb@raw_input()@ or the \verb@readline()@ method of file objects. \obindex{file} \index{input!raw} diff --git a/Doc/ref6.tex b/Doc/ref6.tex index 086d49b..b1d4572 100644 --- a/Doc/ref6.tex +++ b/Doc/ref6.tex @@ -27,14 +27,14 @@ simple_stmt: expression_stmt Expression statements are used (mostly interactively) to compute and write a value, or (usually) to call a procedure (a function that returns no meaningful result; in Python, procedures return the value -\verb\None\): +\verb@None@): \begin{verbatim} expression_stmt: expression_list \end{verbatim} An expression statement evaluates the expression list (which may be a -single expression). If the value is not \verb\None\, it is converted +single expression). If the value is not \verb@None@, it is converted to a string using the rules for string conversions (expressions in reverse quotes), and the resulting string is written to standard output (see section \ref{print}) on a line by itself. @@ -45,9 +45,9 @@ output (see section \ref{print}) on a line by itself. \indexii{standard}{output} \indexii{writing}{values} -(The exception for \verb\None\ is made so that procedure calls, which +(The exception for \verb@None@ is made so that procedure calls, which are syntactically equivalent to expressions, do not cause any output. -A tuple with only \verb\None\ items is written normally.) +A tuple with only \verb@None@ items is written normally.) \indexii{procedure}{call} \section{Assignment statements} @@ -114,7 +114,7 @@ If the target is an identifier (name): \begin{itemize} \item -If the name does not occur in a \verb\global\ statement in the current +If the name does not occur in a \verb@global@ statement in the current code block: the name is bound to the object in the current local name space. \stindex{global} @@ -140,10 +140,10 @@ the corresponding targets. \item If the target is an attribute reference: The primary expression in the reference is evaluated. It should yield an object with assignable -attributes; if this is not the case, \verb\TypeError\ is raised. That +attributes; if this is not the case, \verb@TypeError@ is raised. That object is then asked to assign the assigned object to the given attribute; if it cannot perform the assignment, it raises an exception -(usually but not necessarily \verb\AttributeError\). +(usually but not necessarily \verb@AttributeError@). \indexii{attribute}{assignment} \item @@ -159,7 +159,7 @@ must yield a plain integer. If it is negative, the sequence's length is added to it. The resulting value must be a nonnegative integer less than the sequence's length, and the sequence is asked to assign the assigned object to its item with that index. If the index is out -of range, \verb\IndexError\ is raised (assignment to a subscripted +of range, \verb@IndexError@ is raised (assignment to a subscripted sequence cannot add new items to a list). \obindex{sequence} \obindex{list} @@ -175,16 +175,17 @@ key with the same value existed). \item If the target is a slicing: The primary expression in the reference is -evaluated. It should yield a mutable sequence (list) object. The +evaluated. It should yield a mutable sequence object (e.g. a list). The assigned object should be a sequence object of the same type. Next, the lower and upper bound expressions are evaluated, insofar they are present; defaults are zero and the sequence's length. The bounds should evaluate to (small) integers. If either bound is negative, the sequence's length is added to it. The resulting bounds are clipped to lie between zero and the sequence's length, inclusive. Finally, the -sequence object is asked to replace the items indicated by the slice -with the items of the assigned sequence. This may change the -sequence's length, if it allows it. +sequence object is asked to replace the slice with the items of the +assigned sequence. The length of the slice may be different from the +length of the assigned sequence, thus changing the length of the +target sequence, if the object allows it. \indexii{slicing}{assignment} \end{itemize} @@ -201,7 +202,7 @@ messages.) pass_stmt: "pass" \end{verbatim} -\verb\pass\ is a null operation --- when it is executed, nothing +\verb@pass@ is a null operation --- when it is executed, nothing happens. It is useful as a placeholder when a statement is required syntactically, but no code needs to be executed, for example: \indexii{null}{operation} @@ -230,7 +231,7 @@ to right. Deletion of a name removes the binding of that name (which must exist) from the local or global name space, depending on whether the name -occurs in a \verb\global\ statement in the same code block. +occurs in a \verb@global@ statement in the same code block. \stindex{global} \indexii{unbinding}{name} @@ -247,7 +248,7 @@ right type (but even this is determined by the sliced object). print_stmt: "print" [ condition ("," condition)* [","] ] \end{verbatim} -\verb\print\ evaluates each condition in turn and writes the resulting +\verb@print@ evaluates each condition in turn and writes the resulting object to standard output (see below). If an object is not a string, it is first converted to a string using the rules for string conversions. The (resulting or original) string is then written. A @@ -256,21 +257,21 @@ the output system believes it is positioned at the beginning of a line. This is the case: (1) when no characters have yet been written to standard output; or (2) when the last character written to standard output is \verb/\n/; or (3) when the last write operation on standard -output was not a \verb\print\ statement. (In some cases it may be +output was not a \verb@print@ statement. (In some cases it may be functional to write an empty string to standard output for this reason.) \index{output} \indexii{writing}{values} -A \verb/"\n"/ character is written at the end, unless the \verb\print\ +A \verb/"\n"/ character is written at the end, unless the \verb@print@ statement ends with a comma. This is the only action if the statement -contains just the keyword \verb\print\. +contains just the keyword \verb@print@. \indexii{trailing}{comma} \indexii{newline}{suppression} -Standard output is defined as the file object named \verb\stdout\ -in the built-in module \verb\sys\. If no such object exists, -or if it is not a writable file, a \verb\RuntimeError\ exception is raised. +Standard output is defined as the file object named \verb@stdout@ +in the built-in module \verb@sys@. If no such object exists, +or if it is not a writable file, a \verb@RuntimeError@ exception is raised. (The original implementation attempts to write to the system's original standard output instead, but this is not safe, and should be fixed.) \indexii{standard}{output} @@ -285,19 +286,19 @@ standard output instead, but this is not safe, and should be fixed.) return_stmt: "return" [condition_list] \end{verbatim} -\verb\return\ may only occur syntactically nested in a function +\verb@return@ may only occur syntactically nested in a function definition, not within a nested class definition. \indexii{function}{definition} \indexii{class}{definition} -If a condition list is present, it is evaluated, else \verb\None\ +If a condition list is present, it is evaluated, else \verb@None@ is substituted. -\verb\return\ leaves the current function call with the condition -list (or \verb\None\) as return value. +\verb@return@ leaves the current function call with the condition +list (or \verb@None@) as return value. -When \verb\return\ passes control out of a \verb\try\ statement -with a \verb\finally\ clause, that finally clause is executed +When \verb@return@ passes control out of a \verb@try@ statement +with a \verb@finally@ clause, that finally clause is executed before really leaving the function. \kwindex{finally} @@ -308,14 +309,14 @@ before really leaving the function. raise_stmt: "raise" condition ["," condition] \end{verbatim} -\verb\raise\ evaluates its first condition, which must yield +\verb@raise@ evaluates its first condition, which must yield a string object. If there is a second condition, this is evaluated, -else \verb\None\ is substituted. +else \verb@None@ is substituted. \index{exception} \indexii{raising}{exception} It then raises the exception identified by the first object, -with the second one (or \verb\None\) as its parameter. +with the second one (or \verb@None@) as its parameter. \section{The {\tt break} statement} \stindex{break} @@ -324,22 +325,23 @@ with the second one (or \verb\None\) as its parameter. break_stmt: "break" \end{verbatim} -\verb\break\ may only occur syntactically nested in a \verb\for\ -or \verb\while\ loop, not nested in a function or class definition. +\verb@break@ may only occur syntactically nested in a \verb@for@ +or \verb@while@ loop, but not nested in a function or class definition +within that loop. \stindex{for} \stindex{while} \indexii{loop}{statement} -It terminates the neares enclosing loop, skipping the optional -\verb\else\ clause if the loop has one. +It terminates the nearest enclosing loop, skipping the optional +\verb@else@ clause if the loop has one. \kwindex{else} -If a \verb\for\ loop is terminated by \verb\break\, the loop control +If a \verb@for@ loop is terminated by \verb@break@, the loop control target keeps its current value. \indexii{loop control}{target} -When \verb\break\ passes control out of a \verb\try\ statement -with a \verb\finally\ clause, that finally clause is executed +When \verb@break@ passes control out of a \verb@try@ statement +with a \verb@finally@ clause, that finally clause is executed before really leaving the loop. \kwindex{finally} @@ -350,11 +352,10 @@ before really leaving the loop. continue_stmt: "continue" \end{verbatim} -\verb\continue\ may only occur syntactically nested in a \verb\for\ or -\verb\while\ loop, not nested in a function or class definition, and -not nested in the \verb\try\ clause of a \verb\try\ statement with a -\verb\finally\ clause (it may occur nested in a \verb\except\ or -\verb\finally\ clause of a \verb\try\ statement though). +\verb@continue@ may only occur syntactically nested in a \verb@for@ or +\verb@while@ loop, but not nested in a function or class definition or +\verb@try@ statement within that loop.\footnote{Except that it may +currently occur within an \verb@except@ clause.} \stindex{for} \stindex{while} \indexii{loop}{statement} @@ -373,9 +374,9 @@ import_stmt: "import" identifier ("," identifier)* Import statements are executed in two steps: (1) find a module, and initialize it if necessary; (2) define a name or names in the local -name space (of the scope where the \verb\import\ statement occurs). -The first form (without \verb\from\) repeats these steps for each -identifier in the list, the \verb\from\ form performs them once, with +name space (of the scope where the \verb@import@ statement occurs). +The first form (without \verb@from@) repeats these steps for each +identifier in the list, the \verb@from@ form performs them once, with the first identifier specifying the module name. \indexii{importing}{module} \indexii{name}{binding} @@ -383,15 +384,15 @@ the first identifier specifying the module name. The system maintains a table of modules that have been initialized, indexed by module name. (The current implementation makes this table -accessible as \verb\sys.modules\.) When a module name is found in +accessible as \verb@sys.modules@.) When a module name is found in this table, step (1) is finished. If not, a search for a module definition is started. This first looks for a built-in module definition, and if no built-in module if the given name is found, it searches a user-specified list of directories for a file whose name is -the module name with extension \verb\".py"\. (The current -implementation uses the list of strings \verb\sys.path\ as the search +the module name with extension \verb@".py"@. (The current +implementation uses the list of strings \verb@sys.path@ as the search path; it is initialized from the shell environment variable -\verb\$PYTHONPATH\, with an installation-dependent default.) +\verb@$PYTHONPATH@, with an installation-dependent default.) \ttindex{modules} \ttindex{sys.modules} \indexii{module}{name} @@ -404,9 +405,9 @@ path; it is initialized from the shell environment variable If a built-in module is found, its built-in initialization code is executed and step (1) is finished. If no matching file is found, -\verb\ImportError\ is raised. If a file is found, it is parsed, +\verb@ImportError@ is raised. If a file is found, it is parsed, yielding an executable code block. If a syntax error occurs, -\verb\SyntaxError\ is raised. Otherwise, an empty module of the given +\verb@SyntaxError@ is raised. Otherwise, an empty module of the given name is created and inserted in the module table, and then the code block is executed in the context of this module. Exceptions during this execution terminate step (1). @@ -418,23 +419,23 @@ this execution terminate step (1). When step (1) finishes without raising an exception, step (2) can begin. -The first form of \verb\import\ statement binds the module name in the +The first form of \verb@import@ statement binds the module name in the local name space to the module object, and then goes on to import the -next identifier, if any. The \verb\from\ from does not bind the +next identifier, if any. The \verb@from@ from does not bind the module name: it goes through the list of identifiers, looks each one of them up in the module found in step (1), and binds the name in the local name space to the object thus found. If a name is not found, -\verb\ImportError\ is raised. If the list of identifiers is replaced -by a star (\verb\*\), all names defined in the module are bound, -except those beginning with an underscore(\verb\_\). +\verb@ImportError@ is raised. If the list of identifiers is replaced +by a star (\verb@*@), all names defined in the module are bound, +except those beginning with an underscore(\verb@_@). \indexii{name}{binding} \exindex{ImportError} -Names bound by import statements may not occur in \verb\global\ +Names bound by import statements may not occur in \verb@global@ statements in the same scope. \stindex{global} -The \verb\from\ form with \verb\*\ may only occur in a module scope. +The \verb@from@ form with \verb@*@ may only occur in a module scope. \kwindex{from} \ttindex{from ... import *} @@ -450,19 +451,19 @@ program.) global_stmt: "global" identifier ("," identifier)* \end{verbatim} -The \verb\global\ statement is a declaration which holds for the +The \verb@global@ statement is a declaration which holds for the entire current scope. It means that the listed identifiers are to be interpreted as globals. While {\em using} global names is automatic if they are not defined in the local scope, {\em assigning} to global -names would be impossible without \verb\global\. +names would be impossible without \verb@global@. \indexiii{global}{name}{binding} -Names listed in a \verb\global\ statement must not be used in the same -scope before that \verb\global\ statement is executed. +Names listed in a \verb@global@ statement must not be used in the same +scope before that \verb@global@ statement is executed. -Names listed in a \verb\global\ statement must not be defined as formal -parameters or in a \verb\for\ loop control target, \verb\class\ -definition, function definition, or \verb\import\ statement. +Names listed in a \verb@global@ statement must not be defined as formal +parameters or in a \verb@for@ loop control target, \verb@class@ +definition, function definition, or \verb@import@ statement. (The current implementation does not enforce the latter two restrictions, but programs should not abuse this freedom, as future @@ -478,7 +479,7 @@ access_stmt: "access" ... This statement will be used in the future to control access to instance and class variables. Currently its syntax and effects are -undefined; however the keyword \verb\access\ is a reserved word for +undefined; however the keyword \verb@access@ is a reserved word for the parser. \section{The {\tt exec} statement} \label{exec} @@ -496,12 +497,12 @@ occurs). If it is an open file, the file is parsed until EOF and executed. If it is a code object, it is simply executed. In all cases, if the optional parts are omitted, the code is executed -in the current scope. If only the first expression after \verb\in\ is +in the current scope. If only the first expression after \verb@in@ is specified, it should be a dictionary, which will be used for both the global and the local variables. If two expressions are given, both must be dictionaries and they are used for the global and local variables, respectively. Note: dynamic evaluation of expressions is supported by the built-in -function \verb\eval\. +function \verb@eval@. diff --git a/Doc/ref7.tex b/Doc/ref7.tex index 670eec0..b8babfb9 100644 --- a/Doc/ref7.tex +++ b/Doc/ref7.tex @@ -6,8 +6,8 @@ or control the execution of those other statements in some way. In general, compound statements span multiple lines, although in simple incarnations a whole compound statement may be contained in one line. -The \verb\if\, \verb\while\ and \verb\for\ statements implement -traditional control flow constructs. \verb\try\ specifies exception +The \verb@if@, \verb@while@ and \verb@for@ statements implement +traditional control flow constructs. \verb@try@ specifies exception handlers and/or cleanup code for a group of statements. Function and class definitions are also syntactically compound statements. @@ -21,7 +21,7 @@ statements on the same line as the header, following the header's colon, or it can be one or more indented statements on subsequent lines. Only the latter form of suite can contain nested compound statements; the following is illegal, mostly because it wouldn't be -clear to which \verb\if\ clause a following \verb\else\ clause would +clear to which \verb@if@ clause a following \verb@else@ clause would belong: \index{clause} \index{suite} @@ -32,7 +32,7 @@ if test1: if test2: print x Also note that the semicolon binds tighter than the colon in this context, so that in the following example, either all or none of the -\verb\print\ statements are executed: +\verb@print@ statements are executed: \begin{verbatim} if x < y < z: print x; print y; print z @@ -48,15 +48,15 @@ statement: stmt_list NEWLINE | compound_stmt stmt_list: simple_stmt (";" simple_stmt)* [";"] \end{verbatim} -Note that statements always end in a \verb\NEWLINE\ possibly followed -by a \verb\DEDENT\. +Note that statements always end in a \verb@NEWLINE@ possibly followed +by a \verb@DEDENT@. \index{NEWLINE token} \index{DEDENT token} Also note that optional continuation clauses always begin with a keyword that cannot start a statement, thus there are no ambiguities -(the `dangling \verb\else\' problem is solved in Python by requiring -nested \verb\if\ statements to be indented). +(the `dangling \verb@else@' problem is solved in Python by requiring +nested \verb@if@ statements to be indented). \indexii{dangling}{else} The formatting of the grammar rules in the following sections places @@ -65,7 +65,7 @@ each clause on a separate line for clarity. \section{The {\tt if} statement} \stindex{if} -The \verb\if\ statement is used for conditional execution: +The \verb@if@ statement is used for conditional execution: \begin{verbatim} if_stmt: "if" condition ":" suite @@ -76,8 +76,8 @@ if_stmt: "if" condition ":" suite It selects exactly one of the suites by evaluating the conditions one by one until one is found to be true (see section \ref{Booleans} for the definition of true and false); then that suite is executed (and no -other part of the \verb\if\ statement is executed or evaluated). If -all conditions are false, the suite of the \verb\else\ clause, if +other part of the \verb@if@ statement is executed or evaluated). If +all conditions are false, the suite of the \verb@else@ clause, if present, is executed. \kwindex{elif} \kwindex{else} @@ -86,7 +86,7 @@ present, is executed. \stindex{while} \indexii{loop}{statement} -The \verb\while\ statement is used for repeated execution as long as a +The \verb@while@ statement is used for repeated execution as long as a condition is true: \begin{verbatim} @@ -96,13 +96,13 @@ while_stmt: "while" condition ":" suite This repeatedly tests the condition and, if it is true, executes the first suite; if the condition is false (which may be the first time it -is tested) the suite of the \verb\else\ clause, if present, is +is tested) the suite of the \verb@else@ clause, if present, is executed and the loop terminates. \kwindex{else} -A \verb\break\ statement executed in the first suite terminates the -loop without executing the \verb\else\ clause's suite. A -\verb\continue\ statement executed in the first suite skips the rest +A \verb@break@ statement executed in the first suite terminates the +loop without executing the \verb@else@ clause's suite. A +\verb@continue@ statement executed in the first suite skips the rest of the suite and goes back to testing the condition. \stindex{break} \stindex{continue} @@ -111,7 +111,7 @@ of the suite and goes back to testing the condition. \stindex{for} \indexii{loop}{statement} -The \verb\for\ statement is used to iterate over the elements of a +The \verb@for@ statement is used to iterate over the elements of a sequence (string, tuple or list): \obindex{sequence} @@ -125,16 +125,16 @@ suite is then executed once for each item in the sequence, in the order of ascending indices. Each item in turn is assigned to the target list using the standard rules for assignments, and then the suite is executed. When the items are exhausted (which is immediately -when the sequence is empty), the suite in the \verb\else\ clause, if +when the sequence is empty), the suite in the \verb@else@ clause, if present, is executed, and the loop terminates. \kwindex{in} \kwindex{else} \indexii{target}{list} -A \verb\break\ statement executed in the first suite terminates the -loop without executing the \verb\else\ clause's suite. A -\verb\continue\ statement executed in the first suite skips the rest -of the suite and continues with the next item, or with the \verb\else\ +A \verb@break@ statement executed in the first suite terminates the +loop without executing the \verb@else@ clause's suite. A +\verb@continue@ statement executed in the first suite skips the rest +of the suite and continues with the next item, or with the \verb@else@ clause if there was no next item. \stindex{break} \stindex{continue} @@ -146,9 +146,10 @@ The target list is not deleted when the loop is finished, but if the sequence is empty, it will not have been assigned to at all by the loop. -Hint: the built-in function \verb\range()\ returns a sequence of -integers suitable to emulate the effect of Pascal's \verb\for i := a -to b do\; e.g. \verb\range(3)\ returns the list \verb\[0, 1, 2]\. +Hint: the built-in function \verb@range()@ returns a sequence of +integers suitable to emulate the effect of Pascal's +\verb@for i := a to b do@; +e.g. \verb@range(3)@ returns the list \verb@[0, 1, 2]@. \bifuncindex{range} \index{Pascal} @@ -175,24 +176,25 @@ for x in a[:]: \section{The {\tt try} statement} \label{try} \stindex{try} -The \verb\try\ statement specifies exception handlers and/or cleanup +The \verb@try@ statement specifies exception handlers and/or cleanup code for a group of statements: \begin{verbatim} try_stmt: try_exc_stmt | try_fin_stmt try_exc_stmt: "try" ":" suite ("except" [condition ["," target]] ":" suite)+ + ["else" ":" suite] try_fin_stmt: "try" ":" suite "finally" ":" suite \end{verbatim} -There are two forms of \verb\try\ statement: \verb\try...except\ and -\verb\try...finally\. These forms cannot be mixed. +There are two forms of \verb@try@ statement: \verb@try...except@ and +\verb@try...finally@. These forms cannot be mixed. -The \verb\try...except\ form specifies one or more exception handlers -(the \verb\except\ clauses). When no exception occurs in the -\verb\try\ clause, no exception handler is executed. When an -exception occurs in the \verb\try\ suite, a search for an exception +The \verb@try...except@ form specifies one or more exception handlers +(the \verb@except@ clauses). When no exception occurs in the +\verb@try@ clause, no exception handler is executed. When an +exception occurs in the \verb@try@ suite, a search for an exception handler is started. This inspects the except clauses in turn until one is found that matches the exception. A condition-less except clause, if present, must be last; it matches any exception. For an @@ -211,7 +213,7 @@ handler continues in the surrounding code and on the invocation stack. If the evaluation of a condition in the header of an except clause raises an exception, the original search for a handler is cancelled and a search starts for the new exception in the surrounding code and -on the call stack (it is treated as if the entire \verb\try\ statement +on the call stack (it is treated as if the entire \verb@try@ statement raised the exception). When a matching except clause is found, the exception's parameter is @@ -223,10 +225,10 @@ exception, and the exception occurs in the try clause of the inner handler, the outer handler will not handle the exception.) Before an except clause's suite is executed, details about the -exception are assigned to three variables in the \verb\sys\ module: -\verb\sys.exc_type\ receives the object identifying the exception; -\verb\sys.exc_value\ receives the exception's parameter; -\verb\sys.exc_traceback\ receives a traceback object (see section +exception are assigned to three variables in the \verb@sys@ module: +\verb@sys.exc_type@ receives the object identifying the exception; +\verb@sys.exc_value@ receives the exception's parameter; +\verb@sys.exc_traceback@ receives a traceback object (see section \ref{traceback}) identifying the point in the program where the exception occurred. \bimodindex{sys} @@ -235,20 +237,25 @@ exception occurred. \ttindex{exc_traceback} \obindex{traceback} -The \verb\try...finally\ form specifies a `cleanup' handler. The -\verb\try\ clause is executed. When no exception occurs, the -\verb\finally\ clause is executed. When an exception occurs in the -\verb\try\ clause, the exception is temporarily saved, the -\verb\finally\ clause is executed, and then the saved exception is -re-raised. If the \verb\finally\ clause raises another exception or -executes a \verb\return\, \verb\break\ or \verb\continue\ statement, +The optional \verb@else@ clause is executed when no exception occurs +in the \verb@try@ clause. Exceptions in the \verb@else@ clause are +not handled by the preceding \verb@except@ clauses. +\kwindex{else} + +The \verb@try...finally@ form specifies a `cleanup' handler. The +\verb@try@ clause is executed. When no exception occurs, the +\verb@finally@ clause is executed. When an exception occurs in the +\verb@try@ clause, the exception is temporarily saved, the +\verb@finally@ clause is executed, and then the saved exception is +re-raised. If the \verb@finally@ clause raises another exception or +executes a \verb@return@, \verb@break@ or \verb@continue@ statement, the saved exception is lost. \kwindex{finally} -When a \verb\return\ or \verb\break\ statement is executed in the -\verb\try\ suite of a \verb\try...finally\ statement, the -\verb\finally\ clause is also executed `on the way out'. A -\verb\continue\ statement is illegal in the \verb\try\ clause. (The +When a \verb@return@ or \verb@break@ statement is executed in the +\verb@try@ suite of a \verb@try...finally@ statement, the +\verb@finally@ clause is also executed `on the way out'. A +\verb@continue@ statement is illegal in the \verb@try@ clause. (The reason is a problem with the current implementation --- this restriction may be lifted in the future). \stindex{return} @@ -265,7 +272,8 @@ section \ref{types}): \begin{verbatim} funcdef: "def" funcname "(" [parameter_list] ")" ":" suite -parameter_list: (parameter ",")* ("*" identifier | parameter [","]) +parameter_list: (defparameter ",")* ("*" identifier | defparameter [","]) +defparameter: parameter ["=" condition] sublist: parameter ("," parameter)* [","] parameter: identifier | "(" sublist ")" funcname: identifier @@ -282,8 +290,21 @@ as the global name space to be used when the function is called. The function definition does not execute the function body; this gets executed only when the function is called. +When one or more top-level parameters have the form {\em parameter = +condition}, the function is said to have ``default parameter values''. +Default parameter values are evaluated when the function definition is +executed. For a parameter with a default value, the correponding +argument may be omitted from a call, in which case the parameter's +default value is substituted. If a parameter has a default value, all +following parameters must also have a default value --- this is a +syntactic restriction that is not expressed by the grammar.% +\footnote{Currently this is not checked; instead, +\verb@def f(a=1,b)@ is interpreted as \verb@def f(a=1,b=None)@.} +\indexiii{default}{parameter}{value} + Function call semantics are described in section \ref{calls}. When a -user-defined function is called, the arguments (a.k.a. actual +user-defined function is called, first missing arguments for which a +default value exists are supplied; then the arguments (a.k.a. actual parameters) are bound to the (formal) parameters, as follows: \indexii{function}{call} \indexiii{user-defined}{function}{call} @@ -292,10 +313,6 @@ parameters) are bound to the (formal) parameters, as follows: \indexii{parameter}{formal} \indexii{parameter}{actual} -It is also possible to create anonymous functions (functions not bound -to a name), for immediate use in expressions. This uses lambda forms, -described in section \ref{lambda}. - \begin{itemize} \item @@ -320,7 +337,7 @@ Call this number {\em N}. The first {\em N} arguments are assigned to the corresponding formal parameters in the way descibed above. A tuple containing the remaining arguments, if any, is then assigned to the identifier following the star. This variable will always be a -tuple: if there are no extra arguments, its value is \verb\()\, if +tuple: if there are no extra arguments, its value is \verb@()@, if there is just one extra argument, it is a singleton tuple. \indexii{variable length}{parameter list} @@ -335,6 +352,11 @@ variable length parameter lists are a sufficiently accepted practice in most programming languages that a compromise has been worked out. (And anyway, assignment has no equivalent for empty argument lists.) +It is also possible to create anonymous functions (functions not bound +to a name), for immediate use in expressions. This uses lambda forms, +described in section \ref{lambda}. +\indexii{lambda}{form} + \section{Class definitions} \label{class} \indexii{class}{definition} diff --git a/Doc/ref8.tex b/Doc/ref8.tex index aeb65bf..1ae61ed 100644 --- a/Doc/ref8.tex +++ b/Doc/ref8.tex @@ -13,9 +13,9 @@ While a language specification need not prescribe how the language interpreter is invoked, it is useful to have a notion of a complete Python program. A complete Python program is executed in a minimally initialized environment: all built-in and standard modules are -available, but none have been initialized, except for \verb\sys\ -(various system services), \verb\__builtin__\ (built-in functions, -exceptions and \verb\None\) and \verb\__main__\. The latter is used +available, but none have been initialized, except for \verb@sys@ +(various system services), \verb@__builtin__@ (built-in functions, +exceptions and \verb@None@) and \verb@__main__@. The latter is used to provide the local and global name space for execution of the complete program. \bimodindex{sys} @@ -29,7 +29,7 @@ The interpreter may also be invoked in interactive mode; in this case, it does not read and execute a complete program but reads and executes one statement (possibly compound) at a time. The initial environment is identical to that of a complete program; each statement is executed -in the name space of \verb\__main__\. +in the name space of \verb@__main__@. \index{interactive mode} Under {\UNIX}, a complete program can be passed to the interpreter in @@ -58,7 +58,7 @@ This syntax is used in the following situations: \item when parsing a module; -\item when parsing a string passed to the \verb\exec\ statement; +\item when parsing a string passed to the \verb@exec@ statement; \end{itemize} @@ -80,14 +80,14 @@ end of the input. There are two forms of expression input. Both ignore leading whitespace. -The string argument to \verb\eval()\ must have the following form: +The string argument to \verb@eval()@ must have the following form: \bifuncindex{eval} \begin{verbatim} eval_input: condition_list NEWLINE* \end{verbatim} -The input line read by \verb\input()\ must have the following form: +The input line read by \verb@input()@ must have the following form: \bifuncindex{input} \begin{verbatim} @@ -95,7 +95,7 @@ input_input: condition_list NEWLINE \end{verbatim} Note: to read `raw' input line without interpretation, you can use the -built-in function \verb\raw_input()\ or the \verb\readline()\ method +built-in function \verb@raw_input()@ or the \verb@readline()@ method of file objects. \obindex{file} \index{input!raw} |