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109 lines
3.3 KiB
TeX
109 lines
3.3 KiB
TeX
\chapter{Top-level components}
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The Python interpreter can get its input from a number of sources:
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from a script passed to it as standard input or as program argument,
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typed in interactively, from a module source file, etc. This chapter
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gives the syntax used in these cases.
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\index{interpreter}
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\section{Complete Python programs}
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\index{program}
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While a language specification need not prescribe how the language
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interpreter is invoked, it is useful to have a notion of a complete
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Python program. A complete Python program is executed in a minimally
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initialized environment: all built-in and standard modules are
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available, but none have been initialized, except for \verb\sys\
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(various system services), \verb\builtin\ (built-in functions,
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exceptions and \verb\None\) and \verb\__main__\. The latter is used
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to provide the local and global name space for execution of the
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complete program.
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\bimodindex{sys}
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\bimodindex{__main__}
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\bimodindex{builtin}
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The syntax for a complete Python program is that for file input,
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described in the next section.
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The interpreter may also be invoked in interactive mode; in this case,
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it does not read and execute a complete program but reads and executes
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one statement (possibly compound) at a time. The initial environment
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is identical to that of a complete program; each statement is executed
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in the name space of \verb\__main__\.
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\index{interactive mode}
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Under {\UNIX}, a complete program can be passed to the interpreter in
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three forms: with the {\bf -c} {\it string} command line option, as a
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file passed as the first command line argument, or as standard input.
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If the file or standard input is a tty device, the interpreter enters
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interactive mode; otherwise, it executes the file as a complete
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program.
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\index{UNIX}
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\index{command line}
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\index{standard input}
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\section{File input}
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All input read from non-interactive files has the same form:
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\begin{verbatim}
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file_input: (NEWLINE | statement)*
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\end{verbatim}
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This syntax is used in the following situations:
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\begin{itemize}
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\item when parsing a complete Python program (from a file or from a string);
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\item when parsing a module;
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\item when parsing a string passed to \verb\exec()\;
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\bifuncindex{exec}
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\item when parsing a file passed to \verb\execfile()\;
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\bifuncindex{execfile}
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\end{itemize}
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\section{Interactive input}
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Input in interactive mode is parsed using the following grammar:
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\begin{verbatim}
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interactive_input: [stmt_list] NEWLINE | compound_stmt NEWLINE
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\end{verbatim}
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Note that a (top-level) compound statement must be followed by a blank
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line in interactive mode; this is needed to help the parser detect the
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end of the input.
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\section{Expression input}
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\index{input}
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There are two forms of expression input. Both ignore leading
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whitespace.
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The string argument to \verb\eval()\ must have the following form:
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\bifuncindex{eval}
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\begin{verbatim}
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eval_input: condition_list NEWLINE*
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\end{verbatim}
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The input line read by \verb\input()\ must have the following form:
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\bifuncindex{input}
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\begin{verbatim}
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input_input: condition_list NEWLINE
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\end{verbatim}
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Note: to read `raw' input line without interpretation, you can use the
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built-in function \verb\raw_input()\ or the \verb\readline()\ method
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of file objects.
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\obindex{file}
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\index{input!raw}
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\index{raw input}
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\bifuncindex{raw_index}
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\ttindex{readline}
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