此模块提供标准接口以提取、格式化和打印 Python 程序的堆栈跟踪。它准确模仿 Python 解释器的行为，当打印堆栈跟踪时。这很有用当想要在程序控制下打印堆栈跟踪时，譬如作为在围绕解释器的包裹器。
The module uses traceback objects — this is the object type that is stored in the variables sys.exc_traceback (deprecated) and sys.last_traceback and returned as the third item from sys.exc_info() .
模块定义了下列函数：
打印直到 limit stack trace entries from traceback 。若 limit 被省略或 None ，打印所有条目。若 file 被省略或 None ，输出转到 sys.stderr ；否则它应该是打开文件 (或像文件对象) 以接收输出。
Print exception information and up to limit stack trace entries from traceback to file 。这不同于 print_tb() in the following ways: (1) if traceback 不是 None ，它打印头 回溯 (most recent call last): ; (2) it prints the exception type and value after the stack trace; (3) if type is SyntaxError and value 拥有适当格式，它打印发生句法错误的行，采用插入符号指示错误的大致位置。
这是简写的 print_exception(sys.exc_type, sys.exc_value, sys.exc_traceback, limit, file) . (In fact, it uses sys.exc_info() to retrieve the same information in a thread-safe way instead of using the deprecated variables.)
这像 print_exc(limit) 但返回字符串而不是打印到文件。
2.4 版新增。
这是简写的 print_exception(sys.last_type, sys.last_value, sys.last_traceback, limit, file) 。一般而言，它才工作在异常到达交互提示后 (见 sys.last_type ).
This function prints a stack trace from its invocation point. The optional f 自变量可以用于指定要启动的替代堆栈帧。可选 limit and file 自变量有相同含义如 print_exception() .
Return a list of up to limit “pre-processed” stack trace entries extracted from the traceback object traceback . It is useful for alternate formatting of stack traces. If limit 被省略或 None , all entries are extracted. A “pre-processed” stack trace entry is a 4-tuple ( filename , line number , function name , text ) representing the information that is usually printed for a stack trace. The text is a string with leading and trailing whitespace stripped; if the source is not available it is None .
从当前堆栈帧提取原生回溯。返回值拥有相同的格式如 extract_tb() 。可选 f and limit 自变量有相同含义如 print_stack() .
Given a list of tuples as returned by extract_tb() or 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 None .
Format the exception part of a traceback. The arguments are the exception type and value such as given by sys.last_type and 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 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.
格式化堆栈跟踪和异常信息。自变量拥有的含义如同相应自变量在 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 print_exception() .
简写的 format_list(extract_tb(tb, limit)) .
简写的 format_list(extract_stack(f, limit)) .
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 -O flag was passed to Python the tb.tb_lineno was not updated correctly. This function has no use in versions past 2.3.
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 code 模块。
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)
The following example demonstrates the different ways to print and format the exception and traceback:
import sys, traceback def lumberjack(): bright_side_of_death() def bright_side_of_death(): return tuple()[0] try: lumberjack() except IndexError: exc_type, exc_value, exc_traceback = sys.exc_info() print "*** print_tb:" traceback.print_tb(exc_traceback, limit=1, file=sys.stdout) print "*** print_exception:" traceback.print_exception(exc_type, exc_value, exc_traceback, limit=2, file=sys.stdout) print "*** print_exc:" traceback.print_exc() print "*** format_exc, first and last line:" formatted_lines = traceback.format_exc().splitlines() print formatted_lines[0] print formatted_lines[-1] print "*** format_exception:" print repr(traceback.format_exception(exc_type, exc_value, exc_traceback)) print "*** extract_tb:" print repr(traceback.extract_tb(exc_traceback)) print "*** format_tb:" print repr(traceback.format_tb(exc_traceback)) print "*** tb_lineno:", exc_traceback.tb_lineno
The output for the example would look similar to this:
*** print_tb:
File "<doctest...>", line 10, in <module>
lumberjack()
*** print_exception:
Traceback (most recent call last):
File "<doctest...>", line 10, in <module>
lumberjack()
File "<doctest...>", line 4, in lumberjack
bright_side_of_death()
IndexError: tuple index out of range
*** print_exc:
Traceback (most recent call last):
File "<doctest...>", line 10, in <module>
lumberjack()
File "<doctest...>", line 4, in lumberjack
bright_side_of_death()
IndexError: tuple index out of range
*** format_exc, first and last line:
Traceback (most recent call last):
IndexError: tuple index out of range
*** format_exception:
['Traceback (most recent call last):\n',
' File "<doctest...>", line 10, in <module>\n lumberjack()\n',
' File "<doctest...>", line 4, in lumberjack\n bright_side_of_death()\n',
' File "<doctest...>", line 7, in bright_side_of_death\n return tuple()[0]\n',
'IndexError: tuple index out of range\n']
*** extract_tb:
[('<doctest...>', 10, '<module>', 'lumberjack()'),
('<doctest...>', 4, 'lumberjack', 'bright_side_of_death()'),
('<doctest...>', 7, 'bright_side_of_death', 'return tuple()[0]')]
*** format_tb:
[' File "<doctest...>", line 10, in <module>\n lumberjack()\n',
' File "<doctest...>", line 4, in lumberjack\n bright_side_of_death()\n',
' File "<doctest...>", line 7, in bright_side_of_death\n return tuple()[0]\n']
*** tb_lineno: 10
The following example shows the different ways to print and format the stack:
>>> import traceback >>> def another_function(): ... lumberstack() ... >>> def lumberstack(): ... traceback.print_stack() ... print repr(traceback.extract_stack()) ... print repr(traceback.format_stack()) ... >>> another_function() File "<doctest>", line 10, in <module> another_function() File "<doctest>", line 3, in another_function lumberstack() File "<doctest>", line 6, in lumberstack traceback.print_stack() [('<doctest>', 10, '<module>', 'another_function()'), ('<doctest>', 3, 'another_function', 'lumberstack()'), ('<doctest>', 7, 'lumberstack', 'print repr(traceback.extract_stack())')] [' File "<doctest>", line 10, in <module>\n another_function()\n', ' File "<doctest>", line 3, in another_function\n lumberstack()\n', ' File "<doctest>", line 8, in lumberstack\n print repr(traceback.format_stack())\n']
This last example demonstrates the final few formatting functions:
>>> import traceback >>> traceback.format_list([('spam.py', 3, '<module>', 'spam.eggs()'), ... ('eggs.py', 42, 'eggs', 'return "bacon"')]) [' File "spam.py", line 3, in <module>\n spam.eggs()\n', ' File "eggs.py", line 42, in eggs\n return "bacon"\n'] >>> an_error = IndexError('tuple index out of range') >>> traceback.format_exception_only(type(an_error), an_error) ['IndexError: tuple index out of range\n']