[Python-checkins] CVS: python/dist/src/Doc/ref ref4.tex,1.22,1.23
Jeremy Hylton
jhylton@users.sourceforge.net
Wed, 31 Jan 2001 19:51:01 -0800
Update of /cvsroot/python/python/dist/src/Doc/ref
In directory usw-pr-cvs1:/tmp/cvs-serv5037
Modified Files:
ref4.tex
Log Message:
update section 4.1 to describe nested scopes
Index: ref4.tex
===================================================================
RCS file: /cvsroot/python/python/dist/src/Doc/ref/ref4.tex,v
retrieving revision 1.22
retrieving revision 1.23
diff -C2 -r1.22 -r1.23
*** ref4.tex 2000/04/03 04:41:18 1.22
--- ref4.tex 2001/02/01 03:50:59 1.23
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*** 33,56 ****
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}\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}\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
--- 33,88 ----
information (used for debugging), determines where and how execution
continues after the code block's execution has completed, and (perhaps
! most importantly) defines the environment in which names are resolved.
! A \dfn{namespace}\indexii{namespace} is a mapping from names
! (identifiers) to objects. An \dfn{environment}\index{environment} is
! a hierarchical collection of the namespaces that are visible to a
! particular code block. Python namespaces are statically scoped in the
! tradition of Algol, but also has \keyword{global} statement that can
! be used to access the top-level namespace on the environment.
!
! Names refers to objects. Names are introduced by name
! \dfn{binding}\indexii{binding}{name} operations. Each occurrence of a name
! in the program text refers to the binding of that name established in
! the innermost function namespace containing the use. Changing the
! mapping of a name to an object 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).
! When a name is bound, a mapping is created in the \dfn{local
! namespace}\indexii{local}{namespace} of the execution frame unless the
! name is declared global. If a name binding operation occurs anywhere
! within a code block, all uses of the name within the block are treated
! as references to the local namespace. (Note: This can lead to errors
! when a name is used within a block before it is bound.)
!
! The \dfn{global namespace}\indexii{global}{namespace} determines the
! place where names listed in \keyword{global}\stindex{global}
! statements are defined and searched. The global namespace of a block
! is the namespace of the module in which the block was defined.
!
! If a name is used within a code block, but it is not bound there and
! is not declared global, it is a \dfn{free variable}
! \indexii{free}{variable}. A free variable is resolved using the
! nearest enclosing function block that has a binding for the name. If
! no such block exists, the name is resolved in the global namespace.
+ When a name is not found at all, a
+ \exception{NameError}\withsubitem{(built-in
+ exception)}{\ttindex{NameError}} exception is raised.
+
+ The local namespace of a class definition becomes the attribute
+ dictionary of the class. If a block is contained within a class
+ definition, the name bindings that occur in the containing class block
+ are not visible to enclosed blocks.
+
+ The following constructs bind names: formal parameters to functions,
+ \keyword{import} statements, class and function definitions (these bind
+ the class or function name in the defining block), and identifiers
+ occurring as the target of an assignment, in a \keyword{for} loop header
+ (including list comprehensions), or in the second position of an
+ \keyword{except} clause.
+
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
***************
*** 58,148 ****
in the code block is local in the entire code block; all other names
are considered global. The \keyword{global} statement forces global
! interpretation of selected names throughout the code block. The
! following constructs bind names: formal parameters to functions,
\keyword{import} statements, class and function definitions (these
bind the class or function name in the defining block), and targets
that are identifiers if occurring in an assignment, \keyword{for} loop
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.}
A target occurring in a \keyword{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 namespace, it is
searched in the built-in namespace (which is actually the global
! 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}
-
- The following table lists the meaning of the local and global
- namespace for various types of code blocks. The namespace for a
- particular module is automatically created when the module is first
- 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{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__}\refbimodindex{__main__}}
- {same as global}{(1)}
- \lineiv{Interactive command}
- {n.s. for \module{__main__}\refbimodindex{__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}
-
- Notes:
-
- \begin{description}
-
- \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.''
-
- \item[(2)] The global and local namespace for these can be
- overridden with optional extra arguments.
! \item[(3)] The \keyword{exec} statement and the \function{eval()} and
\function{execfile()} functions have optional arguments to override
the global and local namespace. If only one namespace is specified,
--- 90,137 ----
in the code block is local in the entire code block; all other names
are considered global. The \keyword{global} statement forces global
! interpretation of selected names throughout the code block.
!
! The following constructs bind names: formal parameters to functions,
\keyword{import} statements, class and function definitions (these
bind the class or function name in the defining block), and targets
that are identifiers if occurring in an assignment, \keyword{for} loop
header, or in the second position of an \keyword{except} clause
! header. The \keyword{import} statement of the form ``\samp{from
! \ldots import *}'' binds all names defined in the imported module,
! except those beginning with an underscore. This form may only be used
! at the module level.
A target occurring in a \keyword{del} statement is also considered bound
! for this purpose (though the actual semantics are to unbind the
! name). It is illegal to unbind a name that is referenced by an
! enclosing scope; the compiler will report a \exception{SyntaxError}.
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__}\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.
\stindex{from}
\stindex{exec}
\stindex{global}
! The namespace for a module is automatically created the first time a
! module is imported. The main module for a script is always called
! \module{__main__}\refbimodindex{__main__}.
!
! The \function{eval()}, \function{execfile()}, and \function{input()}
! functions and the \keyword{exec} statement do not have access to the
! full environment for resolving names. Names may be resolved in the
! local and global namespaces of the caller. Free variables are not
! resolved in the nearest enclosing namespaces, but in the global
! namespace.\footnote{This limitation occurs because the code that is
! executed by these operations is not available at the time the
! module is compiled.}
! The \keyword{exec} statement and the \function{eval()} and
\function{execfile()} functions have optional arguments to override
the global and local namespace. If only one namespace is specified,
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*** 151,158 ****
\end{description}
! 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
--- 140,147 ----
\end{description}
! The built-in functions \function{globals()} and \function{locals()}
! each return a dictionary, representing the current global and local
! namespace respectively. The effect of modifications to these
! dictionaries on the namespace are undefined.\footnote{
The current implementations return the dictionary actually used to
implement the namespace, \emph{except} for functions, where the