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[ 587993 ] SET_LINENO killer Remove SET_LINENO. Tracing is now supported by inspecting co_lnotab. Many sundry changes to document and adapt to this change.
151 lines
6.3 KiB
TeX
151 lines
6.3 KiB
TeX
\section{\module{traceback} ---
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Print or retrieve a stack traceback}
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\declaremodule{standard}{traceback}
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\modulesynopsis{Print or retrieve a stack traceback.}
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This module provides a standard interface to extract, format and print
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stack traces of Python programs. It exactly mimics the behavior of
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the Python interpreter when it prints a stack trace. This is useful
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when you want to print stack traces under program control, such as in a
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``wrapper'' around the interpreter.
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The module uses traceback objects --- this is the object type that is
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stored in the variables \code{sys.exc_traceback} (deprecated) and
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\code{sys.last_traceback} and returned as the third item from
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\function{sys.exc_info()}.
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\obindex{traceback}
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The module defines the following functions:
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\begin{funcdesc}{print_tb}{traceback\optional{, limit\optional{, file}}}
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Print up to \var{limit} stack trace entries from \var{traceback}. If
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\var{limit} is omitted or \code{None}, all entries are printed.
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If \var{file} is omitted or \code{None}, the output goes to
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\code{sys.stderr}; otherwise it should be an open file or file-like
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object to receive the output.
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\end{funcdesc}
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\begin{funcdesc}{print_exception}{type, value, traceback\optional{,
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limit\optional{, file}}}
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Print exception information and up to \var{limit} stack trace entries
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from \var{traceback} to \var{file}.
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This differs from \function{print_tb()} in the
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following ways: (1) if \var{traceback} is not \code{None}, it prints a
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header \samp{Traceback (most recent call last):}; (2) it prints the
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exception \var{type} and \var{value} after the stack trace; (3) if
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\var{type} is \exception{SyntaxError} and \var{value} has the
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appropriate format, it prints the line where the syntax error occurred
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with a caret indicating the approximate position of the error.
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\end{funcdesc}
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\begin{funcdesc}{print_exc}{\optional{limit\optional{, file}}}
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This is a shorthand for \code{print_exception(sys.exc_type,
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sys.exc_value, sys.exc_traceback, \var{limit}, \var{file})}. (In
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fact, it uses \function{sys.exc_info()} to retrieve the same
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information in a thread-safe way instead of using the deprecated
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variables.)
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\end{funcdesc}
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\begin{funcdesc}{print_last}{\optional{limit\optional{, file}}}
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This is a shorthand for \code{print_exception(sys.last_type,
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sys.last_value, sys.last_traceback, \var{limit}, \var{file})}.
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\end{funcdesc}
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\begin{funcdesc}{print_stack}{\optional{f\optional{, limit\optional{, file}}}}
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This function prints a stack trace from its invocation point. The
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optional \var{f} argument can be used to specify an alternate stack
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frame to start. The optional \var{limit} and \var{file} arguments have the
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same meaning as for \function{print_exception()}.
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\end{funcdesc}
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\begin{funcdesc}{extract_tb}{traceback\optional{, limit}}
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Return a list of up to \var{limit} ``pre-processed'' stack trace
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entries extracted from the traceback object \var{traceback}. It is
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useful for alternate formatting of stack traces. If \var{limit} is
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omitted or \code{None}, all entries are extracted. A
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``pre-processed'' stack trace entry is a quadruple (\var{filename},
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\var{line number}, \var{function name}, \var{text}) representing
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the information that is usually printed for a stack trace. The
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\var{text} is a string with leading and trailing whitespace
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stripped; if the source is not available it is \code{None}.
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\end{funcdesc}
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\begin{funcdesc}{extract_stack}{\optional{f\optional{, limit}}}
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Extract the raw traceback from the current stack frame. The return
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value has the same format as for \function{extract_tb()}. The
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optional \var{f} and \var{limit} arguments have the same meaning as
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for \function{print_stack()}.
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\end{funcdesc}
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\begin{funcdesc}{format_list}{list}
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Given a list of tuples as returned by \function{extract_tb()} or
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\function{extract_stack()}, return a list of strings ready for
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printing. Each string in the resulting list corresponds to the item
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with the same index in the argument list. Each string ends in a
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newline; the strings may contain internal newlines as well, for those
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items whose source text line is not \code{None}.
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\end{funcdesc}
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\begin{funcdesc}{format_exception_only}{type, value}
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Format the exception part of a traceback. The arguments are the
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exception type and value such as given by \code{sys.last_type} and
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\code{sys.last_value}. The return value is a list of strings, each
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ending in a newline. Normally, the list contains a single string;
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however, for \exception{SyntaxError} exceptions, it contains several
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lines that (when printed) display detailed information about where the
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syntax error occurred. The message indicating which exception
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occurred is the always last string in the list.
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\end{funcdesc}
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\begin{funcdesc}{format_exception}{type, value, tb\optional{, limit}}
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Format a stack trace and the exception information. The arguments
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have the same meaning as the corresponding arguments to
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\function{print_exception()}. The return value is a list of strings,
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each ending in a newline and some containing internal newlines. When
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these lines are concatenated and printed, exactly the same text is
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printed as does \function{print_exception()}.
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\end{funcdesc}
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\begin{funcdesc}{format_tb}{tb\optional{, limit}}
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A shorthand for \code{format_list(extract_tb(\var{tb}, \var{limit}))}.
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\end{funcdesc}
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\begin{funcdesc}{format_stack}{\optional{f\optional{, limit}}}
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A shorthand for \code{format_list(extract_stack(\var{f}, \var{limit}))}.
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\end{funcdesc}
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\begin{funcdesc}{tb_lineno}{tb}
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This function returns the current line number set in the traceback
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object. This function was necessary because in versions of Python
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prior to 2.3 when the \programopt{O} flag was passed to Python the
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\code{\var{tb}.tb_lineno} was not updated correctly. This function
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has no use in versions past 2.3.
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\end{funcdesc}
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\subsection{Traceback Example \label{traceback-example}}
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This simple example implements a basic read-eval-print loop, similar
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to (but less useful than) the standard Python interactive interpreter
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loop. For a more complete implementation of the interpreter loop,
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refer to the \refmodule{code} module.
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\begin{verbatim}
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import sys, traceback
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def run_user_code(envdir):
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source = raw_input(">>> ")
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try:
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exec source in envdir
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except:
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print "Exception in user code:"
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print '-'*60
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traceback.print_exc(file=sys.stdout)
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print '-'*60
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envdir = {}
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while 1:
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run_user_code(envdir)
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\end{verbatim}
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