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Diffstat (limited to 'Doc/ref/ref4.tex')
| -rw-r--r-- | Doc/ref/ref4.tex | 77 |
1 files changed, 42 insertions, 35 deletions
diff --git a/Doc/ref/ref4.tex b/Doc/ref/ref4.tex index 4d5f8d0..aace01f 100644 --- a/Doc/ref/ref4.tex +++ b/Doc/ref/ref4.tex @@ -1,4 +1,4 @@ -\chapter{Execution model} +\chapter{Execution model\label{execmodel}} \index{execution model} \section{Code blocks, execution frames, and namespaces} \label{execframes} @@ -6,7 +6,7 @@ \indexii{execution}{frame} \index{namespace} -A {\em code block} is a piece of Python program text that can be +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 @@ -29,7 +29,7 @@ passed to the built-in function \function{eval()} and to the read and evaluated by the built-in function \function{input()} is a code block. -A code block is executed in an execution frame. An {\em execution +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 @@ -37,11 +37,11 @@ namespaces, the local and the global namespace, that affect execution of the code block. \indexii{execution}{frame} -A {\em namespace} is a mapping from names (identifiers) to objects. +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 {\em binding} a name (to an object); changing the mapping of -a name is called {\em rebinding}; removing a name is {\em unbinding}. +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} @@ -49,8 +49,8 @@ implemented as dictionaries). \indexii{rebinding}{name} \indexii{unbinding}{name} -The {\em local namespace} of an execution frame determines the default -place where names are defined and searched. The {\em global +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. @@ -105,36 +105,43 @@ imported (i.e., when it is loaded). Note that in almost all cases, the global namespace is the namespace of the containing module --- scopes in Python do not nest! -\begin{center} -\begin{tabular}{|l|l|l|l|} -\hline -Code block type & Global namespace & Local namespace & Notes \\ -\hline -Module & n.s. for this module & same as global & \\ -Script (file or command) & n.s. for \module{__main__} & same as global - & (1) \\ -Interactive command & n.s. for \module{__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. & (2) \\ -String passed to \keyword{exec} statement - & global n.s. of containing block - & local n.s. of containing block & (2), (3) \\ -String passed to \function{eval()} - & global n.s. of caller & local n.s. of caller & (2), (3) \\ -File read by \function{execfile()} - & global n.s. of caller & local n.s. of caller & (2), (3) \\ -Expression read by \function{input()} - & global n.s. of caller & local n.s. of caller & \\ -\hline -\end{tabular} -\end{center} +\begin{tableiv}{l|l|l|l}{textrm}% + {Code block type}{Global namespace}{Local namespace}{Notes} + \lineiv{Module}% + {n.s. for this module}% + {same as global}{} + \lineiv{Script (file or command)}% + {n.s. for \module{__main__}}% + {same as global}{(1)} + \lineiv{Interactive command}% + {n.s. for \module{__main__}}% + {same as global}{} + \lineiv{Class definition}% + {global n.s. of containing block}% + {new n.s.}{} + \lineiv{Function body}% + {global n.s. of containing block}% + {new n.s.}{(2)} + \lineiv{String passed to \keyword{exec} statement}% + {global n.s. of containing block}% + {local n.s. of containing block}{(2), (3)} + \lineiv{String passed to \function{eval()}}% + {global n.s. of caller}% + {local n.s. of caller}{(2), (3)} + \lineiv{File read by \function{execfile()}}% + {global n.s. of caller}% + {local n.s. of caller}{(2), (3)} + \lineiv{Expression read by \function{input()}}% + {global n.s. of caller}% + {local n.s. of caller}{} +\end{tableiv} \refbimodindex{__main__} Notes: \begin{description} -\item[n.s.] means {\em namespace} +\item[n.s.] means \emph{namespace} \item[(1)] The main module for a script is always called \module{__main__}; ``the filename don't enter into it.'' @@ -154,7 +161,7 @@ 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, {\em except} for functions, where +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.} @@ -162,8 +169,8 @@ differently, and \function{locals()} returns a read-only dictionary.} 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 {\em raised} at the point where the error -is detected; it may be {\em handled} by the surrounding code block or +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} |