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
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
|
\section{\module{traceback} ---
Print or retrieve a stack traceback}
\declaremodule{standard}{traceback}
\modulesynopsis{Print or retrieve a stack traceback.}
This module provides a standard interface to extract, format and print
stack traces of Python programs. It exactly mimics the behavior of
the Python interpreter when it prints a stack trace. This is useful
when you want to print stack traces under program control, such as in a
``wrapper'' around the interpreter.
The module uses traceback objects --- this is the object type that is
stored in the variables \code{sys.exc_traceback} (deprecated) and
\code{sys.last_traceback} and returned as the third item from
\function{sys.exc_info()}.
\obindex{traceback}
The module defines the following functions:
\begin{funcdesc}{print_tb}{traceback\optional{, limit\optional{, file}}}
Print up to \var{limit} stack trace entries from \var{traceback}. If
\var{limit} is omitted or \code{None}, all entries are printed.
If \var{file} is omitted or \code{None}, the output goes to
\code{sys.stderr}; otherwise it should be an open file or file-like
object to receive the output.
\end{funcdesc}
\begin{funcdesc}{print_exception}{type, value, traceback\optional{,
limit\optional{, file}}}
Print exception information and up to \var{limit} stack trace entries
from \var{traceback} to \var{file}.
This differs from \function{print_tb()} in the
following ways: (1) if \var{traceback} is not \code{None}, it prints a
header \samp{Traceback (most recent call last):}; (2) it prints the
exception \var{type} and \var{value} after the stack trace; (3) if
\var{type} is \exception{SyntaxError} and \var{value} has the
appropriate format, it prints the line where the syntax error occurred
with a caret indicating the approximate position of the error.
\end{funcdesc}
\begin{funcdesc}{print_exc}{\optional{limit\optional{, file}}}
This is a shorthand for \code{print_exception(sys.exc_type,
sys.exc_value, sys.exc_traceback, \var{limit}, \var{file})}. (In
fact, it uses \function{sys.exc_info()} to retrieve the same
information in a thread-safe way instead of using the deprecated
variables.)
\end{funcdesc}
\begin{funcdesc}{format_exc}{\optional{limit\optional{, file}}}
This is like \code{print_exc(\var{limit})} but returns a string
instead of printing to a file.
\versionadded{2.4}
\end{funcdesc}
\begin{funcdesc}{print_last}{\optional{limit\optional{, file}}}
This is a shorthand for \code{print_exception(sys.last_type,
sys.last_value, sys.last_traceback, \var{limit}, \var{file})}.
\end{funcdesc}
\begin{funcdesc}{print_stack}{\optional{f\optional{, limit\optional{, file}}}}
This function prints a stack trace from its invocation point. The
optional \var{f} argument can be used to specify an alternate stack
frame to start. The optional \var{limit} and \var{file} arguments have the
same meaning as for \function{print_exception()}.
\end{funcdesc}
\begin{funcdesc}{extract_tb}{traceback\optional{, limit}}
Return a list of up to \var{limit} ``pre-processed'' stack trace
entries extracted from the traceback object \var{traceback}. It is
useful for alternate formatting of stack traces. If \var{limit} is
omitted or \code{None}, all entries are extracted. A
``pre-processed'' stack trace entry is a quadruple (\var{filename},
\var{line number}, \var{function name}, \var{text}) representing
the information that is usually printed for a stack trace. The
\var{text} is a string with leading and trailing whitespace
stripped; if the source is not available it is \code{None}.
\end{funcdesc}
\begin{funcdesc}{extract_stack}{\optional{f\optional{, limit}}}
Extract the raw traceback from the current stack frame. The return
value has the same format as for \function{extract_tb()}. The
optional \var{f} and \var{limit} arguments have the same meaning as
for \function{print_stack()}.
\end{funcdesc}
\begin{funcdesc}{format_list}{list}
Given a list of tuples as returned by \function{extract_tb()} or
\function{extract_stack()}, return a list of strings ready for
printing. Each string in the resulting list corresponds to the item
with the same index in the argument list. Each string ends in a
newline; the strings may contain internal newlines as well, for those
items whose source text line is not \code{None}.
\end{funcdesc}
\begin{funcdesc}{format_exception_only}{type, value}
Format the exception part of a traceback. The arguments are the
exception type and value such as given by \code{sys.last_type} and
\code{sys.last_value}. The return value is a list of strings, each
ending in a newline. Normally, the list contains a single string;
however, for \exception{SyntaxError} exceptions, it contains several
lines that (when printed) display detailed information about where the
syntax error occurred. The message indicating which exception
occurred is the always last string in the list.
\end{funcdesc}
\begin{funcdesc}{format_exception}{type, value, tb\optional{, limit}}
Format a stack trace and the exception information. The arguments
have the same meaning as the corresponding arguments to
\function{print_exception()}. The return value is a list of strings,
each ending in a newline and some containing internal newlines. When
these lines are concatenated and printed, exactly the same text is
printed as does \function{print_exception()}.
\end{funcdesc}
\begin{funcdesc}{format_tb}{tb\optional{, limit}}
A shorthand for \code{format_list(extract_tb(\var{tb}, \var{limit}))}.
\end{funcdesc}
\begin{funcdesc}{format_stack}{\optional{f\optional{, limit}}}
A shorthand for \code{format_list(extract_stack(\var{f}, \var{limit}))}.
\end{funcdesc}
\begin{funcdesc}{tb_lineno}{tb}
This function returns the current line number set in the traceback
object. This function was necessary because in versions of Python
prior to 2.3 when the \programopt{-O} flag was passed to Python the
\code{\var{tb}.tb_lineno} was not updated correctly. This function
has no use in versions past 2.3.
\end{funcdesc}
\subsection{Traceback Example \label{traceback-example}}
This simple example implements a basic read-eval-print loop, similar
to (but less useful than) the standard Python interactive interpreter
loop. For a more complete implementation of the interpreter loop,
refer to the \refmodule{code} module.
\begin{verbatim}
import sys, traceback
def run_user_code(envdir):
source = raw_input(">>> ")
try:
exec source in envdir
except:
print "Exception in user code:"
print '-'*60
traceback.print_exc(file=sys.stdout)
print '-'*60
envdir = {}
while 1:
run_user_code(envdir)
\end{verbatim}
|
