9. Top-level components顶级组件

The Python interpreter can get its input from a number of sources: from a script passed to it as standard input or as program argument, typed in interactively, from a module source file, etc. Python解释器可以从多个源获取输入：从作为标准输入或作为程序参数传递给它的脚本，以交互方式键入，从模块源文件等。This chapter gives the syntax used in these cases.本章给出了这些情况下使用的语法。

9.1. Complete Python programs完成Python程序

While a language specification need not prescribe how the language interpreter is invoked, it is useful to have a notion of a complete Python program. 虽然语言规范不需要规定如何调用语言解释器，但有一个完整Python程序的概念是很有用的。A complete Python program is executed in a minimally initialized environment: all built-in and standard modules are available, but none have been initialized, except for sys (various system services), builtins (built-in functions, exceptions and None) and __main__. 一个完整的Python程序是在一个最低限度初始化的环境中执行的：所有内置和标准模块都可用，但除了sys（各种系统服务）、builtins（内置函数、异常和None）和__main__之外，没有任何模块已初始化。The latter is used to provide the local and global namespace for execution of the complete program.后者用于为整个程序的执行提供本地和全局命名空间。

The syntax for a complete Python program is that for file input, described in the next section.完整Python程序的语法是用于文件输入的语法，将在下一节中介绍。

The interpreter may also be invoked in interactive mode; in this case, it does not read and execute a complete program but reads and executes one statement (possibly compound) at a time. 解释器也可以在交互模式下调用；在这种情况下，它不会读取并执行一个完整的程序，而是一次读取并执行一条语句（可能是复合语句）。The initial environment is identical to that of a complete program; each statement is executed in the namespace of __main__.初始环境与完整程序的环境相同；每个语句都在__main__的命名空间中执行。

A complete program can be passed to the interpreter in three forms: with the -c string command line option, as a file passed as the first command line argument, or as standard input. 完整的程序可以以三种形式传递给解释器：使用-c字符串命令行选项、作为第一个命令行参数传递的文件或作为标准输入。If the file or standard input is a tty device, the interpreter enters interactive mode; otherwise, it executes the file as a complete program.如果文件或标准输入为tty设备，口译员进入交互模式；否则，它会将文件作为一个完整的程序执行。

9.2. File input文件输入

All input read from non-interactive files has the same form:从非交互式文件读取的所有输入具有相同的形式：


file_input ::=  (NEWLINE | statement)*

This syntax is used in the following situations:此语法用于以下情况：

  • when parsing a complete Python program (from a file or from a string);解析完整的Python程序时（从文件或字符串）；

  • when parsing a module;解析模块时；

  • when parsing a string passed to the exec() function;解析传递给exec()函数的字符串时；

9.3. Interactive input交互式输入

Input in interactive mode is parsed using the following grammar:使用以下语法分析交互式模式中的输入：


interactive_input ::=  [stmt_list] NEWLINE | compound_stmt NEWLINE

Note that a (top-level) compound statement must be followed by a blank line in interactive mode; this is needed to help the parser detect the end of the input.注意，在交互模式下，（顶层）复合语句后面必须跟一个空行；这有助于解析器检测输入的结束。

9.4. Expression input表达式输入

eval() is used for expression input. 用于表达式输入。It ignores leading whitespace. 它忽略前导空格。The string argument to eval() must have the following form:eval()的字符串参数必须具有以下格式：


eval_input ::=  expression_list NEWLINE*