traceback
— 打印或检索堆栈回溯
¶
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。
模块使用回溯对象 — 这种对象类型存储在
sys.last_traceback
变量，且作为第 3 项返回，来自
sys.exc_info()
.
模块定义了下列函数：
traceback.
print_tb
(
traceback
,
limit=None
,
file=None
)
¶
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。
traceback.
print_exception
(
type
,
value
,
traceback
,
limit=None
,
file=None
,
chain=True
)
¶
Print exception information and up to
limit
stack trace entries from
traceback
to
file
。这不同于
print_tb()
在下列方式：
None
，它打印头
Traceback (most recent
call
last):
SyntaxError
and
value
has the appropriate format, it
prints the line where the syntax error occurred with a caret indicating the
approximate position of the error.
若
chain
为 True (默认)，则连锁异常 (
__cause__
or
__context__
属性对于异常) 也将被打印，就像解释器本身在打印未处理异常时所做的。
traceback.
print_exc
(
limit=None
,
file=None
,
chain=True
)
¶
这是简写的
print_exception(*sys.exc_info())
.
traceback.
print_last
(
limit=None
,
file=None
,
chain=True
)
¶
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
).
traceback.
print_stack
(
f=None
,
limit=None
,
file=None
)
¶
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()
.
traceback.
extract_tb
(
traceback
,
limit=None
)
¶
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
.
traceback.
extract_stack
(
f=None
,
limit=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()
.
traceback.
format_list
(
list
)
¶
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
.
traceback.
format_exception_only
(
type
,
value
)
¶
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.
traceback.
format_exception
(
type
,
value
,
tb
,
limit=None
,
chain=True
)
¶
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()
.
traceback.
format_exc
(
limit=None
,
chain=True
)
¶
这像
print_exc(limit)
但返回字符串而不是打印到文件。
traceback.
format_tb
(
tb
,
limit=None
)
¶
简写的
format_list(extract_tb(tb, limit))
.
traceback.
format_stack
(
f=None
,
limit=None
)
¶
简写的
format_list(extract_stack(f, limit))
.
traceback.
clear_frames
(
tb
)
¶
Clears the local variables of all the stack frames in a traceback
tb
通过调用
clear()
method of each frame object.
3.4 版新增。
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 = input(">>> ") try: exec(source, envdir) except Exception: print("Exception in user code:") print("-"*60) traceback.print_exc(file=sys.stdout) print("-"*60) envdir = {} while True: 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']