diff options
Diffstat (limited to 'Doc/ref/ref4.tex')
| -rw-r--r-- | Doc/ref/ref4.tex | 55 |
1 files changed, 34 insertions, 21 deletions
diff --git a/Doc/ref/ref4.tex b/Doc/ref/ref4.tex index 62db120..c14fada 100644 --- a/Doc/ref/ref4.tex +++ b/Doc/ref/ref4.tex @@ -20,9 +20,9 @@ The following are code blocks: A module is a code block. A function body is a code block. A class definition is a code block. Each command typed interactively is a separate code block; a script file is a code block. The string argument passed to the built-in function -\verb\eval\ and to the \verb\exec\ statement are code blocks. +\verb@eval@ and to the \verb@exec@ statement are code blocks. And finally, the -expression read and evaluated by the built-in function \verb\input\ is +expression read and evaluated by the built-in function \verb@input@ is a code block. A code block is executed in an execution frame. An {\em execution @@ -46,7 +46,7 @@ Name spaces are functionally equivalent to dictionaries. The {\em local name space} of an execution frame determines the default place where names are defined and searched. The {\em global name -space} determines the place where names listed in \verb\global\ +space} determines the place where names listed in \verb@global@ statements are defined and searched, and where names that are not explicitly bound in the current code block are searched. \indexii{local}{name space} @@ -55,25 +55,35 @@ explicitly bound in the current code block are searched. Whether a name is local or global in a code block is determined by static inspection of the source text for the code block: in the -absence of \verb\global\ statements, a name that is bound anywhere in +absence of \verb@global@ statements, a name that is bound anywhere in the code block is local in the entire code block; all other names are -considered global. The \verb\global\ statement forces global +considered global. The \verb@global@ statement forces global interpretation of selected names throughout the code block. The -following constructs bind names: formal parameters, \verb\import\ +following constructs bind names: formal parameters, \verb@import@ statements, class and function definitions (these bind the class or function name), and targets that are identifiers if occurring in an -assignment, \verb\for\ loop header, or \verb\except\ clause header. -(A target occurring in a \verb\del\ statement does not bind a name.) +assignment, \verb@for@ loop header, or \verb@except@ clause header. + +A target occurring in a \verb@del@ statement is also considered bound +for this purpose (though the actual semantics are to ``unbind'' the +name). When a global name is not found in the global name space, it is searched in the list of ``built-in'' names (which is actually the -global name space of the module \verb\__builtin__\). When a name is not -found at all, the \verb\NameError\ exception is raised. +global name space of the module \verb@__builtin__@). When a name is not +found at all, the \verb@NameError@ exception is raised.% +\footnote{If the code block contains \verb@exec@ statement or the +construct \verb@from ... import *@, the semantics of names not +explicitly mentioned in a \verb@global@ statement change subtly: name +lookup first searches the local name space, then the global one, then +the built-in one.} The following table lists the meaning of the local and global name space for various types of code blocks. The name space for a particular module is automatically created when the module is first -referenced. +referenced. Note that in almost all cases, the global name space is +the name space of the containing module -- scopes in Python do not +nest! \begin{center} \begin{tabular}{|l|l|l|l|} @@ -81,15 +91,18 @@ referenced. Code block type & Global name space & Local name space & Notes \\ \hline Module & n.s. for this module & same as global & \\ -Script & n.s. for \verb\__main__\ & same as global & \\ -Interactive command & n.s. for \verb\__main__\ & same as global & \\ +Script & n.s. for \verb@__main__@ & same as global & \\ +Interactive command & n.s. for \verb@__main__@ & same as global & \\ Class definition & global n.s. of containing block & new n.s. & \\ Function body & global n.s. of containing block & new n.s. & \\ -String passed to \verb\exec\ or \verb\eval\ +String passed to \verb@exec@ statement + & global n.s. of cobtaining block + & local n.s. of containing block & (1) \\ +String passed to \verb@eval()@ & global n.s. of caller & local n.s. of caller & (1) \\ -File read by \verb\execfile\ +File read by \verb@execfile()@ & global n.s. of caller & local n.s. of caller & (1) \\ -Expression read by \verb\input\ +Expression read by \verb@input@ & global n.s. of caller & local n.s. of caller & \\ \hline \end{tabular} @@ -101,7 +114,7 @@ Notes: \item[n.s.] means {\em name space} -\item[(1)] The global and local name space for these functions can be +\item[(1)] The global and local name space for these can be overridden with optional extra arguments. \end{description} @@ -123,8 +136,8 @@ where the error occurred. The Python interpreter raises an exception when it detects an run-time error (such as division by zero). A Python program can also -explicitly raise an exception with the \verb\raise\ statement. -Exception handlers are specified with the \verb\try...except\ +explicitly raise an exception with the \verb@raise@ statement. +Exception handlers are specified with the \verb@try...except@ statement. Python uses the ``termination'' model of error handling: an exception @@ -139,10 +152,10 @@ execution of the program, or returns to its interactive main loop. Exceptions are identified by string objects. Two different string objects with the same value identify different exceptions. -When an exception is raised, an object (maybe \verb\None\) is passed +When an exception is raised, an object (maybe \verb@None@) is passed as the exception's ``parameter''; this object does not affect the selection of an exception handler, but is passed to the selected exception handler as additional information. -See also the description of the \verb\try\ and \verb\raise\ +See also the description of the \verb@try@ and \verb@raise@ statements. |