Python标准库traceback打印或检索堆栈回溯

  • Z时代
  • 2024-01-10
  • 分类：综合

python lib

源代码： Lib/traceback.py

该模块提供了一个标准接口来提取、格式化和打印 Python 程序的堆栈跟踪结果。它完全模仿Python 解释器在打印堆栈跟踪结果时的行为。当您想要在程序控制下打印堆栈跟踪结果时，例如在“封装”解释器时，这是非常有用的。

这个模块使用 traceback 对象 —— 这是存储在 sys.last_traceback 中的对象类型变量，并作为 sys.exc_info() 的第三项被返回。

这个模块定义了以下函数：

traceback.print_tb(tb, limit=None, file=None)

如果*limit*是正整数，那么从 traceback 对象 "tb" 输出最高 limit 个（从调用函数开始的）栈的堆栈回溯‎条目‎；如果 limit 是负数就输出 abs(limit) 个回溯条目；又如果 limit 被省略或者为 None，那么就会输出所有回溯条目。如果 file 被省略或为 None 那么就会输出至标准输出``sys.stderr``否则它应该是一个打开的文件或者文件类对象来接收输出

在 3.5 版更改: 添加了对负数值 limit 的支持

traceback.print_exception(etype, value, tb, limit=None, file=None, chain=True)

打印回溯对象 tb 到 file 的异常信息和整个堆栈回溯。这和 print_tb() 比有以下方面不同：

  • 如果 tb 不为 None，它将打印头部 Traceback(mostrecentcalllast):

  • 它将在输出完堆栈回溯后，输出异常中的 etype 和 value 信息

  • if type(value) is 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.

The optional limit argument has the same meaning as for print_tb().

If chain is true (the default), then chained exceptions (the

__cause__ or __context__ attributes of the exception) will be

printed as well, like the interpreter itself does when printing an unhandled

exception.

在 3.5 版更改: The etype argument is ignored and inferred from the type of value.

traceback.print_exc(limit=None, file=None, chain=True)

This is a shorthand for print_exception(*sys.exc_info(),limit,file,

chain).

traceback.print_last(limit=None, file=None, chain=True)

This is a shorthand for print_exception(sys.last_type,sys.last_value,

sys.last_traceback,limit,file,chain). In general it will work only

after an exception has reached an interactive prompt (see

sys.last_type).

traceback.print_stack(f=None, limit=None, file=None)

Print up to limit stack trace entries (starting from the invocation

point) if limit is positive. Otherwise, print the last abs(limit)

entries. If limit is omitted or None, all entries are printed.

The optional f argument can be used to specify an alternate stack frame

to start. The optional file argument has the same meaning as for

print_tb().

在 3.5 版更改: 添加了对负数值 limit 的支持

traceback.extract_tb(tb, limit=None)

Return a StackSummary object representing a list of "pre-processed"

stack trace entries extracted from the traceback object tb. It is useful

for alternate formatting of stack traces. The optional limit argument has

the same meaning as for print_tb(). A "pre-processed" stack trace

entry is a FrameSummary object containing attributes

filename, lineno,

name, and line representing the

information that is usually printed for a stack trace. The

line 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)

Extract the raw traceback from the current stack frame. The return value has

the same format as for extract_tb(). The optional f and limit

arguments have the same meaning as for print_stack().

traceback.format_list(extracted_list)

Given a list of tuples or FrameSummary objects 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(etype, 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(etype, value, tb, limit=None, chain=True)

Format a stack trace and the exception information. The arguments have the

same meaning as the corresponding arguments to 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().

在 3.5 版更改: The etype argument is ignored and inferred from the type of value.

traceback.format_exc(limit=None, chain=True)

This is like print_exc(limit) but returns a string instead of printing to

a file.

traceback.format_tb(tb, limit=None)

A shorthand for format_list(extract_tb(tb,limit)).

traceback.format_stack(f=None, limit=None)

A shorthand for format_list(extract_stack(f,limit)).

traceback.clear_frames(tb)

Clears the local variables of all the stack frames in a traceback tb

by calling the clear() method of each frame object.

3.4 新版功能.

traceback.walk_stack(f)

Walk a stack following f.f_back from the given frame, yielding the frame

and line number for each frame. If f is None, the current stack is

used. This helper is used with StackSummary.extract().

3.5 新版功能.

traceback.walk_tb(tb)

Walk a traceback following tb_next yielding the frame and line number

for each frame. This helper is used with StackSummary.extract().

3.5 新版功能.

The module also defines the following classes:

TracebackException Objects¶

3.5 新版功能.

TracebackException objects are created from actual exceptions to

capture data for later printing in a lightweight fashion.

class traceback.TracebackException(exc_type, exc_value, exc_traceback, *, limit=None, lookup_lines=True, capture_locals=False)

Capture an exception for later rendering. limit, lookup_lines and

capture_locals are as for the StackSummary class.

Note that when locals are captured, they are also shown in the traceback.

__cause__

A TracebackException of the original __cause__.

__context__

A TracebackException of the original __context__.

__suppress_context__

The __suppress_context__ value from the original exception.

stack

A StackSummary representing the traceback.

exc_type

The class of the original traceback.

filename

For syntax errors - the file name where the error occurred.

lineno

For syntax errors - the line number where the error occurred.

text

For syntax errors - the text where the error occurred.

offset

For syntax errors - the offset into the text where the error occurred.

msg

For syntax errors - the compiler error message.

classmethod from_exception(exc, *, limit=None, lookup_lines=True, capture_locals=False)

Capture an exception for later rendering. limit, lookup_lines and

capture_locals are as for the StackSummary class.

Note that when locals are captured, they are also shown in the traceback.

format(*, chain=True)

Format the exception.

If chain is not True, __cause__ and __context__ will not

be formatted.

The return value is a generator of strings, each ending in a newline and

some containing internal newlines. print_exception()

is a wrapper around this method which just prints the lines to a file.

The message indicating which exception occurred is always the last

string in the output.

format_exception_only()

Format the exception part of the traceback.

The return value is a generator of strings, each ending in a newline.

Normally, the generator emits a single string; however, for

SyntaxError exceptions, it emits several lines that (when

printed) display detailed information about where the syntax

error occurred.

The message indicating which exception occurred is always the last

string in the output.

StackSummary Objects¶

3.5 新版功能.

StackSummary objects represent a call stack ready for formatting.

class traceback.StackSummary

classmethod extract(frame_gen, *, limit=None, lookup_lines=True, capture_locals=False)

Construct a StackSummary object from a frame generator (such as

is returned by walk_stack() or

walk_tb()).

If limit is supplied, only this many frames are taken from frame_gen.

If lookup_lines is False, the returned FrameSummary

objects will not have read their lines in yet, making the cost of

creating the StackSummary cheaper (which may be valuable if it

may not actually get formatted). If capture_locals is True the

local variables in each FrameSummary are captured as object

representations.

classmethod from_list(a_list)

Construct a StackSummary object from a supplied list of

FrameSummary objects or old-style list of tuples. Each tuple

should be a 4-tuple with filename, lineno, name, line as the elements.

format()

Returns a list of strings ready for printing. Each string in the

resulting list corresponds to a single frame from the stack.

Each string ends in a newline; the strings may contain internal

newlines as well, for those items with source text lines.

For long sequences of the same frame and line, the first few

repetitions are shown, followed by a summary line stating the exact

number of further repetitions.

在 3.6 版更改: Long sequences of repeated frames are now abbreviated.

FrameSummary Objects¶

3.5 新版功能.

FrameSummary objects represent a single frame in a traceback.

class traceback.FrameSummary(filename, lineno, name, lookup_line=True, locals=None, line=None)

Represent a single frame in the traceback or stack that is being formatted

or printed. It may optionally have a stringified version of the frames

locals included in it. If lookup_line is False, the source code is not

looked up until the FrameSummary has the line

attribute accessed (which also happens when casting it to a tuple).

line may be directly provided, and will prevent line

lookups happening at all. locals is an optional local variable

dictionary, and if supplied the variable representations are stored in the

summary for later display.

Traceback Examples¶

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

module.

python3 notranslate">
importsys,traceback
defrun_user_code(envdir):
source=input(">>> ")
try:
exec(source,envdir)
exceptException:
print("Exception in user code:")
print("-"*60)
traceback.print_exc(file=sys.stdout)
print("-"*60)
envdir={}
whileTrue:
run_user_code(envdir)

The following example demonstrates the different ways to print and format the

exception and traceback:

python3 notranslate">
importsys,traceback
deflumberjack():
bright_side_of_death()
defbright_side_of_death():
returntuple()[0]
try:
lumberjack()
exceptIndexError:
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:")
# exc_type below is ignored on 3.5 and later
traceback.print_exception(exc_type,exc_value,exc_traceback,
limit=2,file=sys.stdout)
print("*** print_exc:")
traceback.print_exc(limit=2,file=sys.stdout)
print("*** format_exc, first and last line:")
formatted_lines=traceback.format_exc().splitlines()
print(formatted_lines[0])
print(formatted_lines[-1])
print("*** format_exception:")
# exc_type below is ignored on 3.5 and later
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:
[<FrameSummary file <doctest...>, line 10 in <module>>,
 <FrameSummary file <doctest...>, line 4 in lumberjack>,
 <FrameSummary file <doctest...>, line 7 in bright_side_of_death>]
*** 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:

>>> importtraceback
>>> defanother_function():
... lumberstack()
...
>>> deflumberstack():
... 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:

>>> importtraceback
>>> 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']

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