# `traceback` — Print or retrieve a stack traceback

소스 코드: Lib/traceback.py

This module provides a standard interface to extract, format and print stack traces of Python programs. It is more flexible than the interpreter’s default traceback display, and therefore makes it possible to configure certain aspects of the output. Finally, it contains a utility for capturing enough information about an exception to print it later, without the need to save a reference to the actual exception. Since exceptions can be the roots of large objects graph, this utility can significantly improve memory management.

The module uses traceback objects — these are objects of type `types.TracebackType`, which are assigned to the `__traceback__` field of `BaseException` instances.

더 보기

Module `faulthandler`

  Used to dump Python tracebacks explicitly, on a fault, after a timeout, or on a user signal.

Module `pdb`

  Interactive source code debugger for Python programs.

The module’s API can be divided into two parts:

- Module-level functions offering basic functionality, which are useful for interactive inspection of exceptions and tracebacks.

- `TracebackException` class and its helper classes `StackSummary` and `FrameSummary`. These offer both more flexibility in the output generated and the ability to store the information necessary for later formatting without holding references to actual exception and traceback objects.

## Module-Level Functions

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

  Print up to limit stack trace entries from traceback object tb (starting from the caller’s frame) if limit is positive. Otherwise, print the last `abs(limit)` entries. If limit is omitted or `None`, all entries are printed. If file is omitted or `None`, the output goes to `sys.stderr`; otherwise it should be an open file or file-like object to receive the output.

  참고

  The meaning of the limit parameter is different than the meaning of `sys.tracebacklimit`. A negative limit value corresponds to a positive value of `sys.tracebacklimit`, whereas the behaviour of a positive limit value cannot be achieved with `sys.tracebacklimit`.

  버전 3.5에서 변경: 음수 limit 지원을 추가했습니다.

traceback.print_exception(exc, /, [value, tb, ]limit=None, file=None, chain=True)

  Print exception information and stack trace entries from traceback object tb to file. This differs from `print_tb()` in the following ways:

  - tb가 `None`이 아니면, 헤더 `Traceback (most recent call last):`를 인쇄합니다.

  - it prints the exception type and value after the stack trace

  - type(value)가 `SyntaxError`고 value가 적절한 형식을 가지면, 에러의 대략적인 위치를 나타내는 캐럿(caret)과 함께 문법 에러가 발생한 줄을 인쇄합니다.

  Since Python 3.10, instead of passing value and tb, an exception object can be passed as the first argument. If value and tb are provided, the first argument is ignored in order to provide backwards compatibility.

  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.

  버전 3.5에서 변경: etype 인자는 무시되고 value 형에서 유추됩니다.

  버전 3.10에서 변경: The etype parameter has been renamed to exc and is now positional-only.

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

  This is a shorthand for `print_exception(sys.exception(), limit, file, chain)`.

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

  This is a shorthand for `print_exception(sys.last_exc, limit, file, chain)`. In general it will work only after an exception has reached an interactive prompt (see `sys.last_exc`).

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()`.

  버전 3.5에서 변경: 음수 limit 지원을 추가했습니다.

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.

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.print_list(extracted_list, file=None)

  Print the list of tuples as returned by `extract_tb()` or `extract_stack()` as a formatted stack trace to the given file. If file is `None`, the output is written to `sys.stderr`.

traceback.format_list(extracted_list)

  `extract_tb()`나 `extract_stack()`이 반환한 튜플이나 `FrameSummary` 객체의 리스트가 제공되면, 인쇄할 준비가 된 문자열의 리스트를 반환합니다. 결과 리스트의 각 문자열은 인자 리스트에서 같은 인덱스를 가진 항목에 해당합니다. 각 문자열은 줄 바꿈으로 끝납니다; 소스 텍스트 줄이 `None`이 아닌 항목의 경우, 문자열에 내부 줄 바꿈도 포함될 수 있습니다.

traceback.format_exception_only(exc, /[, value])

  Format the exception part of a traceback using an exception value such as given by `sys.last_value`. The return value is a list of strings, each ending in a newline. The list contains the exception’s message, which is normally a single string; however, for `SyntaxError` exceptions, it contains several lines that (when printed) display detailed information about where the syntax error occurred. Following the message, the list contains the exception’s `notes`.

  Since Python 3.10, instead of passing value, an exception object can be passed as the first argument. If value is provided, the first argument is ignored in order to provide backwards compatibility.

  버전 3.10에서 변경: The etype parameter has been renamed to exc and is now positional-only.

  버전 3.11에서 변경: The returned list now includes any `notes` attached to the exception.

traceback.format_exception(exc, /, [value, tb, ]limit=None, chain=True)

  스택 트레이스와 예외 정보를 포맷합니다. 인자는 `print_exception()`의 해당하는 인자와 같은 의미입니다. 반환 값은 각각 줄 바꿈으로 끝나고 일부는 내부 줄 바꿈을 포함하는 문자열의 리스트입니다. 이 줄들을 이어붙여서 인쇄하면, `print_exception()`과 정확히 같은 텍스트가 인쇄됩니다.

  버전 3.5에서 변경: etype 인자는 무시되고 value 형에서 유추됩니다.

  버전 3.10에서 변경: This function’s behavior and signature were modified to match `print_exception()`.

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

  이것은 `print_exc(limit)`와 비슷하지만, 파일로 인쇄하는 대신 문자열을 반환합니다.

traceback.format_tb(tb, limit=None)

  `format_list(extract_tb(tb, limit))`의 줄임 표현입니다.

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

  `format_list(extract_stack(f, limit))`의 줄임 표현입니다.

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.

  Added in version 3.4.

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()`.

  Added in version 3.5.

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()`.

  Added in version 3.5.

## `TracebackException` Objects

Added in version 3.5.

`TracebackException` objects are created from actual exceptions to capture data for later printing. They offer a more lightweight method of storing this information by avoiding holding references to traceback and frame objects. In addition, they expose more options to configure the output compared to the module-level functions described above.

class traceback.TracebackException(exc_type, exc_value, exc_traceback, *, limit=None, lookup_lines=True, capture_locals=False, compact=False, max_group_width=15, max_group_depth=10)

  Capture an exception for later rendering. The meaning of limit, lookup_lines and capture_locals are as for the `StackSummary` class.

  If compact is true, only data that is required by `TracebackException`’s `format()` method is saved in the class attributes. In particular, the `__context__` field is calculated only if `__cause__` is `None` and `__suppress_context__` is false.

  locals가 포착되면, 트레이스백에도 표시됨에 유의하십시오.

  max_group_width and max_group_depth control the formatting of exception groups (see `BaseExceptionGroup`). The depth refers to the nesting level of the group, and the width refers to the size of a single exception group’s exceptions array. The formatted output is truncated when either limit is exceeded.

  버전 3.10에서 변경: Added the compact parameter.

  버전 3.11에서 변경: Added the max_group_width and max_group_depth parameters.

  __cause__

    A `TracebackException` of the original `__cause__`.

  __context__

    A `TracebackException` of the original `__context__`.

  exceptions

    If `self` represents an `ExceptionGroup`, this field holds a list of `TracebackException` instances representing the nested exceptions. Otherwise it is `None`.

    Added in version 3.11.

  __suppress_context__

    The `__suppress_context__` value from the original exception.

  __notes__

    The `__notes__` value from the original exception, or `None` if the exception does not have any notes. If it is not `None` is it formatted in the traceback after the exception string.

    Added in version 3.11.

  stack

    트레이스백을 나타내는 `StackSummary`.

  exc_type

    원래 트레이스백의 클래스.

  filename

    문법 에러일 때 - 에러가 발생한 파일 이름.

  lineno

    문법 에러일 때 - 에러가 발생한 줄 번호.

  end_lineno

    For syntax errors - the end line number where the error occurred. Can be `None` if not present.

    Added in version 3.10.

  text

    문법 에러일 때 - 에러가 발생한 텍스트.

  offset

    문법 에러일 때 - 에러가 발생한 텍스트에서의 오프셋.

  end_offset

    For syntax errors - the end offset into the text where the error occurred. Can be `None` if not present.

    Added in version 3.10.

  msg

    문법 에러일 때 - 컴파일러 에러 메시지.

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

    나중에 렌더링하기 위해 예외를 포착합니다. limit, lookup_lines 및 capture_locals는 `StackSummary` 클래스와 같습니다.

    locals가 포착되면, 트레이스백에도 표시됨에 유의하십시오.

  print(*, file=None, chain=True)

    Print to file (default `sys.stderr`) the exception information returned by `format()`.

    Added in version 3.11.

  format(*, chain=True)

    예외를 포맷합니다.

    If chain is not `True`, `__cause__` and `__context__` will not be formatted.

    반환 값은 각각 줄 바꿈으로 끝나고 일부는 내부 줄 바꿈을 포함하는 문자열의 제너레이터입니다. `print_exception()`은 단지 파일에 줄을 인쇄하는 이 메서드를 둘러싸는 래퍼입니다.

  format_exception_only()

    트레이스백의 예외 부분을 포맷합니다.

    반환 값은 각각 줄 바꿈으로 끝나는 문자열의 제너레이터입니다.

    The generator emits the exception’s message followed by its notes (if it has any). The exception message is normally a single string; however, for `SyntaxError` exceptions, it consists of several lines that (when printed) display detailed information about where the syntax error occurred.

    버전 3.11에서 변경: The exception’s `notes` are now included in the output.

## `StackSummary` Objects

Added in version 3.5.

`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.

    버전 3.12에서 변경: Exceptions raised from `repr()` on a local variable (when capture_locals is `True`) are no longer propagated to the caller.

  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.

    같은 프레임과 줄의 긴 시퀀스의 경우, 처음 몇 번의 반복이 표시된 다음, 정확한 추가의 반복 횟수를 나타내는 요약 줄이 표시됩니다.

    버전 3.6에서 변경: 반복되는 프레임의 긴 시퀀스가 이제 축약됩니다.

  format_frame_summary(frame_summary)

    Returns a string for printing one of the frames involved in the stack. This method is called for each `FrameSummary` object to be printed by `StackSummary.format()`. If it returns `None`, the frame is omitted from the output.

    Added in version 3.11.

## `FrameSummary` Objects

Added in version 3.5.

A `FrameSummary` object represents a single frame in a traceback.

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

  Represents a single frame in the traceback or stack that is being formatted or printed. It may optionally have a stringified version of the frame’s 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.

  `FrameSummary` instances have the following attributes:

  filename

    The filename of the source code for this frame. Equivalent to accessing `f.f_code.co_filename` on a frame object f.

  lineno

    The line number of the source code for this frame.

  name

    Equivalent to accessing `f.f_code.co_name` on a frame object f.

  line

    A string representing the source code for this frame, with leading and trailing whitespace stripped. If the source is not available, it is `None`.

## Examples of Using the Module-Level Functions

이 간단한 예제는 표준 파이썬 대화식 인터프리터 루프와 비슷하지만 (하지만 덜 유용한) 기본적인 읽기-평가-인쇄 루프를 구현합니다. 인터프리터 루프의 더욱 완전한 구현은 `code` 모듈을 참조하십시오.

    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)

다음 예제는 예외와 추적을 인쇄하고 포맷하는 다양한 방법을 보여줍니다:

    import sys, traceback

    def lumberjack():
        bright_side_of_life()

    def bright_side_of_life():
        return tuple()[0]

    try:
        lumberjack()
    except IndexError as exc:
        print("*** print_tb:")
        traceback.print_tb(exc.__traceback__, limit=1, file=sys.stdout)
        print("*** print_exception:")
        traceback.print_exception(exc, 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:")
        print(repr(traceback.format_exception(exc)))
        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)

예제의 출력은 다음과 유사합니다:

    *** 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_life()
    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_life()
    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 default[0]>", line 10, in <module>\n    lumberjack()\n',
     '  File "<doctest default[0]>", line 4, in lumberjack\n    bright_side_of_life()\n',
     '  File "<doctest default[0]>", line 7, in bright_side_of_life\n    return tuple()[0]\n           ~~~~~~~^^^\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_life>]
    *** format_tb:
    ['  File "<doctest default[0]>", line 10, in <module>\n    lumberjack()\n',
     '  File "<doctest default[0]>", line 4, in lumberjack\n    bright_side_of_life()\n',
     '  File "<doctest default[0]>", line 7, in bright_side_of_life\n    return tuple()[0]\n           ~~~~~~~^^^\n']
    *** tb_lineno: 10

다음 예제는 스택을 인쇄하고 포맷하는 다양한 방법을 보여줍니다:

    >>> 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']

이 마지막 예제는 마지막 몇 가지 포매팅 함수를 예시합니다:

    >>> 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(an_error)
    ['IndexError: tuple index out of range\n']

## Examples of Using `TracebackException`

With the helper class, we have more options:

    >>> import sys
    >>> from traceback import TracebackException
    >>>
    >>> def lumberjack():
    ...     bright_side_of_life()
    ...
    >>> def bright_side_of_life():
    ...     t = "bright", "side", "of", "life"
    ...     return t[5]
    ...
    >>> try:
    ...     lumberjack()
    ... except IndexError as e:
    ...     exc = e
    ...
    >>> try:
    ...     try:
    ...         lumberjack()
    ...     except:
    ...         1/0
    ... except Exception as e:
    ...     chained_exc = e
    ...
    >>> # limit works as with the module-level functions
    >>> TracebackException.from_exception(exc, limit=-2).print()
    Traceback (most recent call last):
      File "<python-input-1>", line 6, in lumberjack
        bright_side_of_life()
        ~~~~~~~~~~~~~~~~~~~^^
      File "<python-input-1>", line 10, in bright_side_of_life
        return t[5]
               ~^^^
    IndexError: tuple index out of range

    >>> # capture_locals adds local variables in frames
    >>> TracebackException.from_exception(exc, limit=-2, capture_locals=True).print()
    Traceback (most recent call last):
      File "<python-input-1>", line 6, in lumberjack
        bright_side_of_life()
        ~~~~~~~~~~~~~~~~~~~^^
      File "<python-input-1>", line 10, in bright_side_of_life
        return t[5]
               ~^^^
        t = ("bright", "side", "of", "life")
    IndexError: tuple index out of range

    >>> # The *chain* kwarg to print() controls whether chained
    >>> # exceptions are displayed
    >>> TracebackException.from_exception(chained_exc).print()
    Traceback (most recent call last):
      File "<python-input-19>", line 4, in <module>
        lumberjack()
        ~~~~~~~~~~^^
      File "<python-input-8>", line 7, in lumberjack
        bright_side_of_life()
        ~~~~~~~~~~~~~~~~~~~^^
      File "<python-input-8>", line 11, in bright_side_of_life
        return t[5]
               ~^^^
    IndexError: tuple index out of range

    During handling of the above exception, another exception occurred:

    Traceback (most recent call last):
      File "<python-input-19>", line 6, in <module>
        1/0
        ~^~
    ZeroDivisionError: division by zero

    >>> TracebackException.from_exception(chained_exc).print(chain=False)
    Traceback (most recent call last):
      File "<python-input-19>", line 6, in <module>
        1/0
        ~^~
    ZeroDivisionError: division by zero