Python 2.7 Tutorial —— 解释器

.. _tut-interacting:

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Interactive Input Editing and History Substitution

***************************************************

Some versions of the Python interpreter support editing of the current input

line and history substitution, similar to facilities found in the Korn shell and

the GNU Bash shell. This is implemented using the `GNU Readline`_ library,

which supports Emacs-style and vi-style editing. This library has its own

documentation which I won't duplicate here; however, the basics are easily

explained. The interactive editing and history described here are optionally

available in the Unix and Cygwin versions of the interpreter.

有些版本的 Python 解释器支持输入行编辑和历史回溯，类似 Korn shell 和

GNU bash shell 的功能。这是通过 `GNU Readline`_ 库实现的。它支持 Emacs

风格和 vi 风格的编辑。这个库有它自己的文档，在此不重复了。不过，基本的

东西很容易演示。交互式编辑和历史查阅在 Unix 和 Cygwin 版中是可选项。

This chapter does *not* document the editing facilities of Mark Hammond's

PythonWin package or the Tk-based environment, IDLE, distributed with Python.

The command line history recall which operates within DOS boxes on NT and some

other DOS and Windows flavors is yet another beast.

本章 *不是* 马克 哈密尔顿的 PythonWin 包和随 Python 发布的基于 TK 的

IDLE 环境的文档。 NT 系统和其它 DOS、Windows 系统上的 DOS 窗中的命令行

历史回调，属于另一个话题。

.. _tut-lineediting:

Line Editing 行编辑

========================

If supported, input line editing is active whenever the interpreter prints a

primary or secondary prompt. The current line can be edited using the

conventional Emacs control characters. The most important of these are:

:kbd:`C-A` (Control-A) moves the cursor to the beginning of the line, :kbd:`C-E`

to the end, :kbd:`C-B` moves it one position to the left, :kbd:`C-F` to the

right. Backspace erases the character to the left of the cursor, :kbd:`C-D` the

character to its right. :kbd:`C-K` kills (erases) the rest of the line to the

right of the cursor, :kbd:`C-Y` yanks back the last killed string.

:kbd:`C-underscore` undoes the last change you made; it can be repeated for

cumulative effect.

如果支持，无论解释器打印主提示符或从属提示符，行编辑都会激活。当前行可

以用 Emacs 风格的快捷键编辑。其中最重要的是： :kbd:`C-A` （Control-A）

将光标移动到行首，　:kbd:`C-E` 移动到行尾， :kbd:`C-B` 向左移一个字

符， :kbd:`C-F` 向右移一位。退格向左删除一个符串， :kbd:`C-D` 向右删除

一个字符。 :kbd:`C-K` 删掉光标右边直到行尾的所有字符， :kbd:`C-Y` 将最

后一次删除的字符串粘贴到光标位置。 :kbd:`C-underscore` （underscores　

即下划线，译注）撤销最后一次修改，它可以因积累作用重复。

.. _tut-history:

History Substitution 历史回溯

====================================================

History substitution works as follows. All non-empty input lines issued are

saved in a history buffer, and when a new prompt is given you are positioned on

a new line at the bottom of this buffer. :kbd:`C-P` moves one line up (back) in

the history buffer, :kbd:`C-N` moves one down. Any line in the history buffer

can be edited; an asterisk appears in front of the prompt to mark a line as

modified. Pressing the :kbd:`Return` key passes the current line to the

interpreter. :kbd:`C-R` starts an incremental reverse search; :kbd:`C-S` starts

a forward search.

历史代替可以工作。所有非空的输入行都被保存在历史缓存中，获得一个新的提

示符的时候，你处于这个缓存的最底的空行。 :kbd:`C-P` 在历史缓存中上溯一

行， :kbd:`C-N` 向下移一行。历史缓存中的任一行都可以编辑；按下

　:kbd:`Return` 键时将当前行传入解释器。 :kbd:`C-R` 开始一个增量向前搜

索；:kbd:`C-S` 开始一个向后搜索。

.. _tut-keybindings:

Key Bindings 快捷键绑定

=============================

The key bindings and some other parameters of the Readline library can be

customized by placing commands in an initialization file called

:file:`~/.inputrc`. Key bindings have the form :

Readline 库的快捷键绑定和其它一些参数可以通过名为 :file:`~/.inputrc`

的初始化文件的替换命名来定制。快捷键绑定如下形式 ::

key-name: function-name

or :

或 ::

"string": function-name

and options can be set with :

选项可以如下设置 ::

set option-name value

For example:

例如 ::

# I prefer vi-style editing:

set editing-mode vi

# Edit using a single line:

set horizontal-scroll-mode On

# Rebind some keys:

Meta-h: backward-kill-word

"/C-u": universal-argument

"/C-x/C-r": re-read-init-file

Note that the default binding for :kbd:`Tab` in Python is to insert a :kbd:`Tab`

character instead of Readline's default filename completion function. If you

insist, you can override this by putting :

需要注意的是 Python 中默认 :kbd:`Tab` 绑定为插入一个 :kbd:`Tab` 字符

而不是 Readline 库的默认文件名完成函数，如果你想用这个，可以将以下内容

插入 ::

Tab: complete

in your :file:`~/.inputrc`. (Of course, this makes it harder to type indented

continuation lines if you're accustomed to using :kbd:`Tab` for that purpose.)

到你的 :file:`~/.inputrc` 中来覆盖它。（当然，如果你真的把 :kbd:`Tab`

设置成这样，就很难在后继行中插入缩进。）

.. index::

module: rlcompleter

module: readline

Automatic completion of variable and module names is optionally available. To

enable it in the interpreter's interactive mode, add the following to your

startup file: [#]_ :

自动完成变量和模块名也可以激活生效。要使之在解释器交互模式中可用，在你

的启动文件中加入下面内容: [#]_ ::

import rlcompleter, readline

readline.parse_and_bind('tab: complete')

This binds the :kbd:`Tab` key to the completion function, so hitting the

:kbd:`Tab` key twice suggests completions; it looks at Python statement names,

the current local variables, and the available module names. For dotted

expressions such as ``string.a``, it will evaluate the expression up to the

final ``'.'`` and then suggest completions from the attributes of the resulting

object. Note that this may execute application-defined code if an object with a

:meth:`__getattr__` method is part of the expression.

这个操作将 :kbd:`Tab` 绑定到完成函数，故按 :kbd:`Tab` 键两次会给出建议

的完成内容；它查找　Python 命名、当前的局部变量、有效的模块名。对于类

似 ``string.a`` 这样的文件名，它会解析 ``'.'`` 相关的表达式，从返回的

结果对象中获取属性，以提供完成建议。需要注意的是，如果对象的

:meth:`__getattr__` 方法是此表达式的一部分，这可能会执行应用程序定

义代码。

A more capable startup file might look like this example. Note that this

deletes the names it creates once they are no longer needed; this is done since

the startup file is executed in the same namespace as the interactive commands,

and removing the names avoids creating side effects in the interactive

environment. You may find it convenient to keep some of the imported modules,

such as :mod:`os`, which turn out to be needed in most sessions with the

interpreter. :

更有用的初始化文件可能是下面这个例子这样的。要注意一旦创建的名字没用

了，它会删掉它们；因为初始化文件作为解释命令与之在同一个命名空间执行，

在交互环境中删除命名带来了边际效应。可能你发现了它体贴的保留了一些导入

模块，类似 :mod:`os` ，在解释器的大多数使用场合中都会用到它们。 ::

# Add auto-completion and a stored history file of commands to your Python

# interactive interpreter. Requires Python 2.0+, readline. Autocomplete is

# bound to the Esc key by default (you can change it - see readline docs).

#

# Store the file in ~/.pystartup, and set an environment variable to point

# to it: "export PYTHONSTARTUP=/home/user/.pystartup" in bash.

#

# Note that PYTHONSTARTUP does *not* expand "~", so you have to put in the

# full path to your home directory.

import atexit

import os

import readline

import rlcompleter

historyPath = os.path.expanduser("~/.pyhistory")

def save_history(historyPath=historyPath):

import readline

readline.write_history_file(historyPath)

if os.path.exists(historyPath):

readline.read_history_file(historyPath)

atexit.register(save_history)

del os, atexit, readline, rlcompleter, save_history, historyPath

.. _tut-commentary:

Alternatives to the Interactive Interpreter 其它交互式解释器

====================================================================================

This facility is an enormous step forward compared to earlier versions of the

interpreter; however, some wishes are left: It would be nice if the proper

indentation were suggested on continuation lines (the parser knows if an indent

token is required next). The completion mechanism might use the interpreter's

symbol table. A command to check (or even suggest) matching parentheses,

quotes, etc., would also be useful.

跟早先版本的解释器比，现在已经有了很大的进步。不过，还是有些期待没有完

成：它应该在后继行中优美的提供缩进（解释器知道下一行是否需要缩

进）建议。完成机制可以使用解释器的符号表。命名检查（或进一步建议）匹配

括号、引号等等。

One alternative enhanced interactive interpreter that has been around for quite

some time is `IPython`_, which features tab completion, object exploration and

advanced history management. It can also be thoroughly customized and embedded

into other applications. Another similar enhanced interactive environment is

`bpython`_.

另有一个强化交互式解释器已经存在一段时间了，它就是 `IPython`，

它支持 tab 完成，对象浏览和高级历史管理。它也可以完全定制或嵌入到其它

应用程序中。另一个类似的强化交互环境是　`bpython`。

.. rubric:: Footnotes

.. [#] Python will execute the contents of a file identified by the

:envvar:`PYTHONSTARTUP` environment variable when you start an interactive

interpreter.

.. [#] 启动交互解释器时，Python 可以执行 :envvar:`PYTHONSTARTUP` 环境变量所指

定的文件内容。

.. _GNU Readline: http://tiswww.case.edu/php/chet/readline/rltop.html
.. _IPython: http://ipython.scipy.org/
.. _bpython: http://www.bpython-interpreter.org/