130 lines
5.4 KiB
TeX
130 lines
5.4 KiB
TeX
\section{Built-in Module \sectcode{sys}}
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\bimodindex{sys}
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This module provides access to some variables used or maintained by the
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interpreter and to functions that interact strongly with the interpreter.
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It is always available.
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\renewcommand{\indexsubitem}{(in module sys)}
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\begin{datadesc}{argv}
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The list of command line arguments passed to a Python script.
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\code{sys.argv[0]} is the script name.
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If no script name was passed to the Python interpreter,
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\code{sys.argv} is empty.
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\end{datadesc}
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\begin{datadesc}{builtin_module_names}
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A list of strings giving the names of all modules that are compiled
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into this Python interpreter. (This information is not available in
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any other way --- \code{sys.modules.keys()} only lists the imported
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modules.)
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\end{datadesc}
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\begin{datadesc}{exc_type}
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\dataline{exc_value}
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\dataline{exc_traceback}
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These three variables are not always defined; they are set when an
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exception handler (an \code{except} clause of a \code{try} statement) is
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invoked. Their meaning is: \code{exc_type} gets the exception type of
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the exception being handled; \code{exc_value} gets the exception
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parameter (its \dfn{associated value} or the second argument to
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\code{raise}); \code{exc_traceback} gets a traceback object which
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encapsulates the call stack at the point where the exception
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originally occurred.
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\end{datadesc}
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\begin{funcdesc}{exit}{n}
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Exit from Python with numeric exit status \var{n}. This is
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implemented by raising the \code{SystemExit} exception, so cleanup
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actions specified by \code{finally} clauses of \code{try} statements
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are honored, and it is possible to catch the exit attempt at an outer
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level.
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\end{funcdesc}
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\begin{datadesc}{exitfunc}
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This value is not actually defined by the module, but can be set by
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the user (or by a program) to specify a clean-up action at program
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exit. When set, it should be a parameterless function. This function
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will be called when the interpreter exits in any way (but not when a
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fatal error occurs: in that case the interpreter's internal state
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cannot be trusted).
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\end{datadesc}
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\begin{datadesc}{last_type}
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\dataline{last_value}
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\dataline{last_traceback}
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These three variables are not always defined; they are set when an
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exception is not handled and the interpreter prints an error message
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and a stack traceback. Their intended use is to allow an interactive
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user to import a debugger module and engage in post-mortem debugging
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without having to re-execute the command that cause the error (which
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may be hard to reproduce). The meaning of the variables is the same
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as that of \code{exc_type}, \code{exc_value} and \code{exc_tracaback},
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respectively.
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\end{datadesc}
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\begin{datadesc}{modules}
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Gives the list of modules that have already been loaded.
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This can be manipulated to force reloading of modules and other tricks.
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\end{datadesc}
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\begin{datadesc}{path}
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A list of strings that specifies the search path for modules.
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Initialized from the environment variable \code{PYTHONPATH}, or an
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installation-dependent default.
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\end{datadesc}
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\begin{datadesc}{ps1}
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\dataline{ps2}
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Strings specifying the primary and secondary prompt of the
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interpreter. These are only defined if the interpreter is in
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interactive mode. Their initial values in this case are
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\code{'>>> '} and \code{'... '}.
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\end{datadesc}
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\begin{funcdesc}{settrace}{tracefunc}
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Set the system's trace function, which allows you to implement a
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Python source code debugger in Python. The standard modules
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\code{pdb} and \code{wdb} are such debuggers; the difference is that
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\code{wdb} uses windows and needs STDWIN, while \code{pdb} has a
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line-oriented interface not unlike dbx. See the file \file{pdb.doc}
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in the Python library source directory for more documentation (both
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about \code{pdb} and \code{sys.trace}).
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\end{funcdesc}
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\ttindex{pdb}
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\ttindex{wdb}
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\index{trace function}
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\begin{funcdesc}{setprofile}{profilefunc}
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Set the system's profile function, which allows you to implement a
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Python source code profiler in Python. The system's profile function
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is called similarly to the system's trace function (see
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\code{sys.settrace}), but it isn't called for each executed line of
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code (only on call and return and when an exception occurs). Also,
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its return value is not used, so it can just return \code{None}.
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\end{funcdesc}
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\index{profile function}
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\begin{datadesc}{stdin}
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\dataline{stdout}
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\dataline{stderr}
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File objects corresponding to the interpreter's standard input,
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output and error streams. \code{sys.stdin} is used for all
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interpreter input except for scripts but including calls to
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\code{input()} and \code{raw_input()}. \code{sys.stdout} is used
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for the output of \code{print} and expression statements and for the
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prompts of \code{input()} and \code{raw_input()}. The interpreter's
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own prompts and (almost all of) its error messages go to
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\code{sys.stderr}. \code{sys.stdout} and \code{sys.stderr} needn't
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be built-in file objects: any object is acceptable as long as it has
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a \code{write} method that takes a string argument.
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\end{datadesc}
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\begin{datadesc}{tracebacklimit}
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When this variable is set to an integer value, it determines the
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maximum number of levels of traceback information printed when an
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unhandled exception occurs. The default is 1000. When set to 0 or
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less, all traceback information is suppressed and only the exception
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type and value are printed.
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\end{datadesc}
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