# cpython / Doc / ref8.tex

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 \chapter{Top-level components} 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} \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 \verb\sys\ (various system services), \verb\__builtin__\ (built-in functions, exceptions and \verb\None\) and \verb\__main__\. The latter is used to provide the local and global name space for execution of the complete program. \bimodindex{sys} \bimodindex{__main__} \bimodindex{__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 name space of \verb\__main__\. \index{interactive mode} Under {\UNIX}, a complete program can be passed to the interpreter in three forms: with the {\bf -c} {\it 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} All input read from non-interactive files has the same form: \begin{verbatim} file_input: (NEWLINE | statement)* \end{verbatim} 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 \verb\exec\ statement; \end{itemize} \section{Interactive input} Input in interactive mode is parsed using the following grammar: \begin{verbatim} interactive_input: [stmt_list] NEWLINE | compound_stmt NEWLINE \end{verbatim} 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} \index{input} There are two forms of expression input. Both ignore leading whitespace. The string argument to \verb\eval()\ must have the following form: \bifuncindex{eval} \begin{verbatim} eval_input: condition_list NEWLINE* \end{verbatim} The input line read by \verb\input()\ must have the following form: \bifuncindex{input} \begin{verbatim} input_input: condition_list NEWLINE \end{verbatim} Note: to read raw' input line without interpretation, you can use the built-in function \verb\raw_input()\ or the \verb\readline()\ method of file objects. \obindex{file} \index{input!raw} \index{raw input} \bifuncindex{raw_index} \ttindex{readline} `