109 lines
3.3 KiB
TeX
109 lines
3.3 KiB
TeX
\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 \verb\exec()\;
|
|
\bifuncindex{exec}
|
|
|
|
\item when parsing a file passed to \verb\execfile()\;
|
|
\bifuncindex{execfile}
|
|
|
|
\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}
|