mirror of https://github.com/python/cpython
Revise the markup so that this formats and uses markup consistently with
the rest of the documentation.
This commit is contained in:
parent
dfdac1af4d
commit
39778b705d
|
@ -1,22 +1,24 @@
|
||||||
\chapter{Appendix: Future statements and nested scopes}
|
\chapter{Future statements and nested scopes \label{futures}}
|
||||||
|
\sectionauthor{Jeremy Hylton}{jeremy@alum.mit.edu}
|
||||||
|
|
||||||
|
|
||||||
The semantics of Python's static scoping will change in version 2.2 to
|
The semantics of Python's static scoping will change in version 2.2 to
|
||||||
support resolution of unbound local names in enclosing functions'
|
support resolution of unbound local names in enclosing functions'
|
||||||
namespaces. The new semantics will be available in Python 2.1 through
|
namespaces. The new semantics will be available in Python 2.1 through
|
||||||
the use of a future statement. This appendix documents these two
|
the use of a ``future'' statement. This appendix documents these two
|
||||||
features for Python 2.1; it will be removed in Python 2.2 and the
|
features for Python 2.1; it will be removed in Python 2.2 and the
|
||||||
features will be documented in the main sections of this manual.
|
features will be documented in the main sections of this manual.
|
||||||
|
|
||||||
\section{Future statements}
|
|
||||||
\indexii{future}{statement}
|
|
||||||
|
|
||||||
A \dfn{future statement} is a directive to the compiler that a
|
\section{Future statements \label{future-statements}}
|
||||||
particular module should be compiled using syntax or semantics that
|
|
||||||
will be available in a specified future release of Python. The future
|
A \dfn{future statement}\indexii{future}{statement} is a directive to
|
||||||
statement is intended to ease migration to future versions of Python
|
the compiler that a particular module should be compiled using syntax
|
||||||
that introduce incompatible changes to the language. It allows use of
|
or semantics that will be available in a specified future release of
|
||||||
the new features on a per-module basis before the release in which the
|
Python. The future statement is intended to ease migration to future
|
||||||
feature becomes standard.
|
versions of Python that introduce incompatible changes to the
|
||||||
|
language. It allows use of the new features on a per-module basis
|
||||||
|
before the release in which the feature becomes standard.
|
||||||
|
|
||||||
\begin{verbatim}
|
\begin{verbatim}
|
||||||
future_statement: "from" "__future__" "import" feature ["as" name]
|
future_statement: "from" "__future__" "import" feature ["as" name]
|
||||||
|
@ -52,7 +54,7 @@ defined, and raises a compile-time error if a future statement contains
|
||||||
a feature not known to it.
|
a feature not known to it.
|
||||||
|
|
||||||
The direct runtime semantics are the same as for any import statement:
|
The direct runtime semantics are the same as for any import statement:
|
||||||
there is a standard module \file{__future__.py}, described later, and
|
there is a standard module \module{__future__}, described later, and
|
||||||
it will be imported in the usual way at the time the future statement
|
it will be imported in the usual way at the time the future statement
|
||||||
is executed.
|
is executed.
|
||||||
|
|
||||||
|
@ -65,17 +67,17 @@ Note that there is nothing special about the statement:
|
||||||
import __future__ [as name]
|
import __future__ [as name]
|
||||||
\end{verbatim}
|
\end{verbatim}
|
||||||
|
|
||||||
That is not a future statement; it's an ordinary import statement, with
|
That is not a future statement; it's an ordinary import statement with
|
||||||
no special semantics or syntax restrictions.
|
no special semantics or syntax restrictions.
|
||||||
|
|
||||||
Code compiled by an exec statement or calls to the builtin functions
|
Code compiled by an exec statement or calls to the builtin functions
|
||||||
\function{compile} and \function{execfile} that occur in a module M
|
\function{compile()} and \function{execfile()} that occur in a module
|
||||||
containing a future statement will use the new syntax or semantics
|
\module{M} containing a future statement will use the new syntax or
|
||||||
associated with the future statement.
|
semantics associated with the future statement.
|
||||||
|
|
||||||
A future statement typed at an interactive interpreter prompt will
|
A future statement typed at an interactive interpreter prompt will
|
||||||
take effect for the rest of the interpreter session. If an
|
take effect for the rest of the interpreter session. If an
|
||||||
interpreter is started with the \emph{-i} option, is passed a
|
interpreter is started with the \programopt{-i} option, is passed a
|
||||||
script name to execute, and the script includes a future statement, it
|
script name to execute, and the script includes a future statement, it
|
||||||
will be in effect in the interactive session started after the script
|
will be in effect in the interactive session started after the script
|
||||||
is executed.
|
is executed.
|
||||||
|
@ -83,10 +85,10 @@ is executed.
|
||||||
\section{\module{__future__} ---
|
\section{\module{__future__} ---
|
||||||
Future statement definitions}
|
Future statement definitions}
|
||||||
|
|
||||||
\declaremodule{standard}{__future__}
|
\declaremodule[future]{standard}{__future__}
|
||||||
\modulesynopsis{Future statement definitions}
|
\modulesynopsis{Future statement definitions}
|
||||||
|
|
||||||
\file{__future__.py} is a real module, and serves three purposes:
|
\module{__future__} is a real module, and serves three purposes:
|
||||||
|
|
||||||
\begin{itemize}
|
\begin{itemize}
|
||||||
|
|
||||||
|
@ -95,13 +97,13 @@ is executed.
|
||||||
|
|
||||||
\item To ensure that future_statements run under releases prior to 2.1
|
\item To ensure that future_statements run under releases prior to 2.1
|
||||||
at least yield runtime exceptions (the import of
|
at least yield runtime exceptions (the import of
|
||||||
\code{__future__} will fail, because there was no module of
|
\module{__future__} will fail, because there was no module of
|
||||||
that name prior to 2.1).
|
that name prior to 2.1).
|
||||||
|
|
||||||
\item To document when incompatible changes were introduced, and when they
|
\item To document when incompatible changes were introduced, and when they
|
||||||
will be --- or were --- made mandatory. This is a form of executable
|
will be --- or were --- made mandatory. This is a form of executable
|
||||||
documentation, and can be inspected programatically via importing
|
documentation, and can be inspected programatically via importing
|
||||||
\code{__future__} and examining its contents.
|
\module{__future__} and examining its contents.
|
||||||
|
|
||||||
\end{itemize}
|
\end{itemize}
|
||||||
|
|
||||||
|
@ -111,8 +113,8 @@ Each statment in \file{__future__.py} is of the form:
|
||||||
FeatureName = "_Feature(" OptionalRelease "," MandatoryRelease ")"
|
FeatureName = "_Feature(" OptionalRelease "," MandatoryRelease ")"
|
||||||
\end{verbatim}
|
\end{verbatim}
|
||||||
|
|
||||||
where, normally, OptionalRelease < MandatoryRelease, and both are
|
where, normally, OptionalRelease is less then MandatoryRelease, and
|
||||||
5-tuples of the same form as \code{sys.version_info}:
|
both are 5-tuples of the same form as \code{sys.version_info}:
|
||||||
|
|
||||||
\begin{verbatim}
|
\begin{verbatim}
|
||||||
(PY_MAJOR_VERSION, # the 2 in 2.1.0a3; an int
|
(PY_MAJOR_VERSION, # the 2 in 2.1.0a3; an int
|
||||||
|
@ -135,15 +137,17 @@ language; in releases at or after that, modules no longer need a
|
||||||
future statement to use the feature in question, but may continue to
|
future statement to use the feature in question, but may continue to
|
||||||
use such imports.
|
use such imports.
|
||||||
|
|
||||||
MandatoryRelease may also be None, meaning that a planned feature got
|
MandatoryRelease may also be \code{None}, meaning that a planned
|
||||||
dropped.
|
feature got dropped.
|
||||||
|
|
||||||
Instances of class \class{_Feature} have two corresponding methods,
|
Instances of class \class{_Feature} have two corresponding methods,
|
||||||
\member{getOptionalRelease()} and \member{getMandatoryRelease()}.
|
\method{getOptionalRelease()} and \method{getMandatoryRelease()}.
|
||||||
|
|
||||||
No feature line will ever be deleted from \file{__future__.py}.
|
No feature description will ever be deleted from \module{__future__}.
|
||||||
|
|
||||||
|
|
||||||
|
\section{Nested scopes \label{nested-scopes}}
|
||||||
|
|
||||||
\section{Nested scopes}
|
|
||||||
\indexii{nested}{scopes}
|
\indexii{nested}{scopes}
|
||||||
|
|
||||||
Nested scopes are left as an exercise for the reader.
|
Nested scopes are left as an exercise for the reader.
|
||||||
|
|
Loading…
Reference in New Issue