2.1 调用解释器 Invoking the Interpreter

The Python interpreter is usually installed as /usr/local/bin/python on those machines where it is available; putting /usr/local/bin in your Unix shell's search path makes it possible to start it by typing the command

通常 Python 的解释器被安装在目标机器的 /usr/local/bin/python 目录下；把 /usr/local/bin 目录放进你的Unix Shell 的搜索路径里，确保它可以通过输入

python

to the shell. Since the choice of the directory where the interpreter lives is an installation option, other places are possible; check with your local Python guru or system administrator. (E.g., /usr/local/python is a popular alternative location.)

来启动。因为安装路径是可选的，所以也有可能安装在其它位置，你可以与安装 Python 的用户或系统管理员联系。（例如，/usr/local/python就是一个很常见的选择）

Typing an end-of-file character (Control-D on Unix, Control-Z on Windows) at the primary prompt causes the interpreter to exit with a zero exit status. If that doesn't work, you can exit the interpreter by typing the following commands: "import sys; sys.exit()".

输入一个文件结束符（Unix上是Ctrl+D，Windows上是Ctrl+Z）解释器会以0值退出（就是说，没有什么错误，正常退出－－译者）。如果这没有起作用，你可以输入以下命令退出："import sys; sys.exit()"。

The interpreter's line-editing features usually aren't very sophisticated. On Unix, whoever installed the interpreter may have enabled support for the GNU readline library, which adds more elaborate interactive editing and history features. Perhaps the quickest check to see whether command line editing is supported is typing Control-P to the first Python prompt you get. If it beeps, you have command line editing; see Appendix A for an introduction to the keys. If nothing appears to happen, or if P is echoed, command line editing isn't available; you'll only be able to use backspace to remove characters from the current line.

解释器的行编辑功能并不很复杂。装在Unix上的解释器可能会有GNU readline 库支持，这样就可以额外得到精巧的交互编辑和历史记录功能。可能检查命令行编辑器支持能力最方便的方式是在主提示符下输入Ctrl-P。如果有嘟嘟声（计算机扬声器），说明你可以使用命令行编辑功能，从附录 A A 可以查到快捷键的介绍。如果什么也没有发声，或者P显示了出来，说明命令行编辑功能不可用，你只有用退格键删掉输入的命令了。

The interpreter operates somewhat like the Unix shell: when called with standard input connected to a tty device, it reads and executes commands interactively; when called with a file name argument or with a file as standard input, it reads and executes a script from that file.

解释器的操作有些像 Unix Shell：使用终端设备做为标准输入来调用它时，解释器交互的解读和执行命令，通过文件名参数或以文件做为标准输入设备时，它从文件中解读并执行脚本。

A second way of starting the interpreter is "python -c command [arg] ...", which executes the statement(s) in command, analogous to the shell's -c option. Since Python statements often contain spaces or other characters that are special to the shell, it is best to quote command in its entirety with double quotes.

启动解释器的第二个方法是"python -c command [arg] ..."，这种方法可以在命令行中直接执行语句，等同于Shell的 -c选项。因为Python语句通常会包括空格之类的特殊字符，所以最好把整个语句用双引号包起来。

Note that there is a difference between "python file" and "python <file". In the latter case, input requests from the program, such as calls to input() and raw_input(), are satisfied from file. Since this file has already been read until the end by the parser before the program starts executing, the program will encounter end-of-file immediately. In the former case (which is usually what you want) they are satisfied from whatever file or device is connected to standard input of the Python interpreter.

注意"python file"和"python <file"是有区别的。对于后一种情况，程序中类似于调用 input()raw_input()这样的输入请求，来自于确定的文件。因为在解析器开始执行之前，文件已经完全读入，所以程序指向文件尾。在前一种情况（这通常是你需要的）它们从来自于任何联接到Python解释器的标准输入，无论它们是文件还是其它设备。

When a script file is used, it is sometimes useful to be able to run the script and enter interactive mode afterwards. This can be done by passing -i before the script. (This does not work if the script is read from standard input, for the same reason as explained in the previous paragraph.)

使用脚本文件时，经常会运行脚本然后进入交互模式。这也可以通过在脚本之前加上-i参数来实现。（如果脚本来自标准输入，就不能这样运行，与前一段提到的原因一样。）