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dir: /sys/src/cmd/python/Doc/ref/ref8.tex/
\chapter{Top-level components\label{top-level}} 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. This chapter gives the syntax used in these cases. \index{interpreter} \section{Complete Python programs\label{programs}} \index{program} 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. 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 \module{sys} (various system services), \module{__builtin__} (built-in functions, exceptions and \code{None}) and \module{__main__}. The latter is used to provide the local and global namespace for execution of the complete program. \refbimodindex{sys} \refbimodindex{__main__} \refbimodindex{__builtin__} The syntax for a complete Python program is that for file input, described in the next section. 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. The initial environment is identical to that of a complete program; each statement is executed in the namespace of \module{__main__}. \index{interactive mode} \refbimodindex{__main__} Under \UNIX, a complete program can be passed to the interpreter in three forms: with the \programopt{-c} \var{string} command line option, as a file passed as the first command line argument, or as standard input. If the file or standard input is a tty device, the interpreter enters interactive mode; otherwise, it executes the file as a complete program. \index{UNIX} \index{command line} \index{standard input} \section{File input\label{file-input}} All input read from non-interactive files has the same form: \begin{productionlist} \production{file_input} {(NEWLINE | \token{statement})*} \end{productionlist} This syntax is used in the following situations: \begin{itemize} \item when parsing a complete Python program (from a file or from a string); \item when parsing a module; \item when parsing a string passed to the \keyword{exec} statement; \end{itemize} \section{Interactive input\label{interactive}} Input in interactive mode is parsed using the following grammar: \begin{productionlist} \production{interactive_input} {[\token{stmt_list}] NEWLINE | \token{compound_stmt} NEWLINE} \end{productionlist} 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. \section{Expression input\label{expression-input}} \index{input} There are two forms of expression input. Both ignore leading whitespace. The string argument to \function{eval()} must have the following form: \bifuncindex{eval} \begin{productionlist} \production{eval_input} {\token{expression_list} NEWLINE*} \end{productionlist} The input line read by \function{input()} must have the following form: \bifuncindex{input} \begin{productionlist} \production{input_input} {\token{expression_list} NEWLINE} \end{productionlist} Note: to read `raw' input line without interpretation, you can use the built-in function \function{raw_input()} or the \method{readline()} method of file objects. \obindex{file} \index{input!raw} \index{raw input} \bifuncindex{raw_input} \withsubitem{(file method)}{\ttindex{readline()}}