Small nits around some of the index entries.

When refering to chapters, use \ref, don't hardcode the chapter
number.
This commit is contained in:
Fred Drake 1999-05-13 18:38:11 +00:00
parent ab03215204
commit 431f0ce547
1 changed files with 66 additions and 70 deletions

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@ -1,20 +1,19 @@
\chapter{Execution model\label{execmodel}}
\chapter{Execution model \label{execmodel}}
\index{execution model}
\section{Code blocks, execution frames, and namespaces\label{execframes}}
\section{Code blocks, execution frames, and namespaces \label{execframes}}
\index{code block}
\indexii{execution}{frame}
\index{namespace}
\indexii{execution}{frame}
A \dfn{code block} is a piece of Python program text that can be
executed as a unit, such as a module, a class definition or a function
body. Some code blocks (like modules) are normally executed only once, others
(like function bodies) may be executed many times. Code blocks may
textually contain other code blocks. Code blocks may invoke other
code blocks (that may or may not be textually contained in them) as
part of their execution, e.g., by invoking (calling) a function.
\index{code block}
\indexii{code}{block}
A \dfn{code block}\indexii{code}{block} is a piece
of Python program text that can be executed as a unit, such as a
module, a class definition or a function body. Some code blocks (like
modules) are normally executed only once, others (like function
bodies) may be executed many times. Code blocks may textually contain
other code blocks. Code blocks may invoke other code blocks (that may
or may not be textually contained in them) as part of their execution,
e.g., by invoking (calling) a function.
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
@ -22,7 +21,7 @@ command typed interactively is a separate code block; a script file (a
file given as standard input to the interpreter or specified on the
interpreter command line the first argument) is a code block; a script
command (a command specified on the interpreter command line with the
`\code{-c}' option) is a code block. The file read by the built-in
`\strong{-c}' option) is a code block. The file read by the built-in
function \function{execfile()} is a code block. The string argument
passed to the built-in function \function{eval()} and to the
\keyword{exec} statement is a code block. And finally, the expression
@ -30,33 +29,28 @@ read and evaluated by the built-in function \function{input()} is a
code block.
A code block is executed in an execution frame. An \dfn{execution
frame} contains some administrative information (used for debugging),
determines where and how execution continues after the code block's
execution has completed, and (perhaps most importantly) defines two
namespaces, the local and the global namespace, that affect
execution of the code block.
\indexii{execution}{frame}
frame}\indexii{execution}{frame} contains some administrative
information (used for debugging), determines where and how execution
continues after the code block's execution has completed, and (perhaps
most importantly) defines two namespaces, the local and the global
namespace, that affect execution of the code block.
A \dfn{namespace} is a mapping from names (identifiers) to objects.
A particular namespace may be referenced by more than one execution
frame, and from other places as well. Adding a name to a namespace
is called \dfn{binding} a name (to an object); changing the mapping of
a name is called \dfn{rebinding}; removing a name is \dfn{unbinding}.
Namespaces are functionally equivalent to dictionaries (and often
implemented as dictionaries).
\index{namespace}
\indexii{binding}{name}
\indexii{rebinding}{name}
\indexii{unbinding}{name}
A \dfn{namespace}\index{namespace} is a mapping from names
(identifiers) to objects. A particular namespace may be referenced by
more than one execution frame, and from other places as well. Adding
a name to a namespace is called \dfn{binding}\indexii{binding}{name} a
name (to an object); changing the mapping of a name is called
\dfn{rebinding}\indexii{rebinding}{name}; removing a name is
\dfn{unbinding}\indexii{unbinding}{name}. Namespaces are functionally
equivalent to dictionaries (and often implemented as dictionaries).
The \dfn{local namespace} of an execution frame determines the default
place where names are defined and searched. The \dfn{global
namespace} determines the place where names listed in \keyword{global}
statements are defined and searched, and where names that are not
bound anywhere in the current code block are searched.
\indexii{local}{namespace}
\indexii{global}{namespace}
\stindex{global}
The \dfn{local namespace}\indexii{local}{namespace} of an execution
frame determines the default place where names are defined and
searched. The
\dfn{global namespace}\indexii{global}{namespace} determines the place
where names listed in \keyword{global}\stindex{global} statements are
defined and searched, and where names that are not bound anywhere 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
@ -72,10 +66,10 @@ header, or in the second position of an \keyword{except} clause
header. Local names are searched only on the local namespace; global
names are searched only in the global and built-in
namespace.\footnote{
If the code block contains \keyword{exec} statements or the construct
``\samp{from \ldots import *}'', the semantics of local names change:
local name lookup first searches the local namespace, then the global
namespace and the built-in namespace.}
If the code block contains \keyword{exec} statements or the
construct ``\samp{from \ldots import *}'', the semantics of local
names change: local name lookup first searches the local namespace,
then the global namespace and the built-in namespace.}
A target occurring in a \keyword{del} statement is also considered bound
for this purpose (though the actual semantics are to ``unbind'' the
@ -83,20 +77,21 @@ name).
When a global name is not found in the global namespace, it is
searched in the built-in namespace (which is actually the global
namespace of the module \module{__builtin__}). The built-in namespace
associated with the execution of a code block is actually found by
looking up the name \code{__builtins__} is its global namespace; this
should be a dictionary or a module (in the latter case its dictionary
is used). Normally, the \code{__builtins__} namespace is the
dictionary of the built-in module \module{__builtin__} (note: no `s');
if it isn't, restricted execution mode is in effect. When a name is
not found at all, a \exception{NameError} exception is raised.%
\refbimodindex{__builtin__}
namespace of the module
\module{__builtin__}\refbimodindex{__builtin__}). The built-in
namespace associated with the execution of a code block is actually
found by looking up the name \code{__builtins__} is its global
namespace; this should be a dictionary or a module (in the latter case
its dictionary is used). Normally, the \code{__builtins__} namespace
is the dictionary of the built-in module \module{__builtin__} (note:
no `s'); if it isn't, restricted
execution\indexii{restricted}{execution} mode is in effect. When a
name is not found at all, a
\exception{NameError}\withsubitem{(built-in
exception)}{\ttindex{NameError}} exception is raised.
\stindex{from}
\stindex{exec}
\stindex{global}
\indexii{restricted}{execution}
\withsubitem{(built-in exception)}{\ttindex{NameError}}
The following table lists the meaning of the local and global
namespace for various types of code blocks. The namespace for a
@ -111,10 +106,10 @@ scopes in Python do not nest!
{n.s. for this module}
{same as global}{}
\lineiv{Script (file or command)}
{n.s. for \module{__main__}}
{n.s. for \module{__main__}\refbimodindex{__main__}}
{same as global}{(1)}
\lineiv{Interactive command}
{n.s. for \module{__main__}}
{n.s. for \module{__main__}\refbimodindex{__main__}}
{same as global}{}
\lineiv{Class definition}
{global n.s. of containing block}
@ -135,7 +130,6 @@ scopes in Python do not nest!
{global n.s. of caller}
{local n.s. of caller}{}
\end{tableiv}
\refbimodindex{__main__}
Notes:
@ -160,22 +154,23 @@ The built-in functions \function{globals()} and \function{locals()} returns a
dictionary representing the current global and local namespace,
respectively. The effect of modifications to this dictionary on the
namespace are undefined.\footnote{
The current implementations return the dictionary actually used to
implement the namespace, \emph{except} for functions, where the
optimizer may cause the local namespace to be implemented differently,
and \function{locals()} returns a read-only dictionary.}
The current implementations return the dictionary actually used to
implement the namespace, \emph{except} for functions, where the
optimizer may cause the local namespace to be implemented
differently, and \function{locals()} returns a read-only
dictionary.}
\section{Exceptions\label{exceptions}}
\section{Exceptions \label{exceptions}}
\index{exception}
Exceptions are a means of breaking out of the normal flow of control
of a code block in order to handle errors or other exceptional
conditions. An exception is \emph{raised} at the point where the error
is detected; it may be \emph{handled} by the surrounding code block or
by any code block that directly or indirectly invoked the code block
where the error occurred.
\index{exception}
\index{raise an exception}
\index{handle an exception}
conditions. An exception is
\emph{raised}\index{raise an exception} at the point where the error
is detected; it may be \emph{handled}\index{handle an exception} by
the surrounding code block or by any code block that directly or
indirectly invoked the code block where the error occurred.
\index{exception handler}
\index{errors}
\index{error handling}
@ -197,7 +192,8 @@ code from the top).
When an exception is not handled at all, the interpreter terminates
execution of the program, or returns to its interactive main loop. In
either case, it prints a stack backtrace, except when the exception is
\exception{SystemExit}.\ttindex{SystemExit}
\exception{SystemExit}\withsubitem{(built-in
exception)}{\ttindex{SystemExit}}.
Exceptions are identified by string objects or class instances.
Selection of a matching except clause is based on object identity
@ -215,4 +211,4 @@ exceptions, this object must be an instance of the exception class
being raised.
See also the description of the \keyword{try} and \keyword{raise}
statements in chapter 7.
statements in chapter \ref{compound}.