# `traceback` --- スタックトレースの表示または取得

ソースコード: 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.

参考

`faulthandler` モジュール

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

`pdb` モジュール

  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.

Added in version 3.13: Output is colorized by default and can be controlled using environment variables.

## モジュールレベルの関数

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.

  注釈

  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`.

  バージョン 3.5 で変更: 負の limit がサポートされました。

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

  トレースバックオブジェクト tb から例外の情報とスタックトレースの項目を file に出力します。 この関数は以下の点で `print_tb()` と異なります:

  - tb が `None` でない場合ヘッダ `Traceback (most recent call last):` を出力します

  - スタックトレースの後に例外タイプと value を出力します

  - type(value) が `SyntaxError` であり、 value が適切な形式を持っていれば、そのエラーのおおよその位置を示すマークと共にシンタックスエラーが発生した行が表示されます。

  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.

  オプション引数 limit の意味は `print_tb()` のものと同じです。 chain が真の場合 (デフォルト)、連鎖した例外 (例外の `__cause__` か `__context__` 属性) も出力されます。 これはインタープリタ自身が処理されていない例外を出力するときと同じです。

  バージョン 3.5 で変更: 引数 etype は無視され、 value の型から推論されます。

  バージョン 3.10 で変更: The etype parameter has been renamed to exc and is now positional-only.

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

  `print_exception(sys.exception(), limit=limit, file=file, chain=chain)` の省略表現です。

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

  `print_exception(sys.last_exc, limit=limit, file=file, chain=chain)` の省略表現です。 一般に、例外が対話的なプロンプトに達した後にのみ機能します (`sys.last_exc` 参照)。

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

  limit が正の場合、最大 limit 個のスタックトレース項目 (呼び出し地点から開始) を出力します。 そうでない場合、最新の `abs(limit)` 個を出力します。 limit が省略されるか `None` の場合、すべての項目が出力されます。オプションの f 引数は、開始する スタックフレーム を指定するために用いることができます。オプションの file 引数は `print_tb()` の file 引数と同様の意味を持っています。

  バージョン 3.5 で変更: 負の limit がサポートされました。

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 with attributes representing the information that is usually printed for a stack trace.

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

  現在の スタックフレーム から生のトレースバックを取り出します。戻り値は `extract_tb()` と同じ形式です。オプションの f と limit 引数は `print_stack()` と同じ意味を持ちます。

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()` または `extract_stack()` が返すタプルのリストまたは `FrameSummary` オブジェクトが与えられると、出力の準備を整えた文字列のリストを返します。結果として生じるリストの中の各文字列は、引数リストの中の同じインデックスの要素に対応します。各文字列は末尾に改行が付いています。さらに、ソーステキスト行が `None` でないそれらの要素に対しては、文字列は内部に改行を含んでいるかもしれません。

traceback.format_exception_only(exc, /, [value, ]*, show_group=False)

  Format the exception part of a traceback using an exception value such as given by `sys.last_exc`. 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.

  When show_group is `True`, and the exception is an instance of `BaseExceptionGroup`, the nested exceptions are included as well, recursively, with indentation relative to their nesting depth.

  バージョン 3.10 で変更: The etype parameter has been renamed to exc and is now positional-only.

  バージョン 3.11 で変更: The returned list now includes any `notes` attached to the exception.

  バージョン 3.13 で変更: show_group 引数が追加されました。

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

  スタックトレースと例外情報を書式化します。引数は `print_exception()` の対応する引数と同じ意味を持ちます。戻り値は文字列のリストで、それぞれの文字列は改行で終わり、そのいくつかは内部に改行を含みます。これらの行が連結されて出力される場合は、厳密に `print_exception()` と同じテキストが出力されます。

  バージョン 3.5 で変更: 引数 etype は無視され、 value の型から推論されます。

  バージョン 3.10 で変更: This function's behavior and signature were modified to match `print_exception()`.

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

  これは、`print_exc(limit)` に似ていますが、ファイルに出力する代わりに文字列を返します。

traceback.format_tb(tb, limit=None)

  `format_list(extract_tb(tb, limit))` の省略表現です。

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

  `format_list(extract_stack(f, limit))` の省略表現です。

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.

  バージョン 3.14 で変更: This function previously returned a generator that would walk the stack when first iterated over. The generator returned now is the state of the stack when `walk_stack` is called.

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` オブジェクト

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.

  局所変数がキャプチャされたとき、それらはトレースバックに表示されることに注意してください。

  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.

  バージョン 3.10 で変更: compact 引数が追加されました。

  バージョン 3.11 で変更: max_group_width と max_group_depth 引数が追加されました。

  __cause__

    元々の `__cause__` の `TracebackException`。

  __context__

    元々の `__context__` の `TracebackException`。

  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__

    元々の例外からの `__suppress_context__`。

  __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

    トレースバックを表す `StackSummary`。

  exc_type

    The class of the original exception.

    バージョン 3.13 で非推奨.

  exc_type_str

    String display of the class of the original exception.

    Added in version 3.13.

  filename

    構文エラー用 - エラーが発生したファイルの名前。

  lineno

    構文エラー用 - エラーが発生した行番号。

  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

    構文エラー用 - エラーが発生したテクスト。

  offset

    構文エラー用 - エラーが発生したテクストへのオフセット。

  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

    構文エラー用 - コンパイラのエラーメッセージ。

  classmethod from_exception(exc, *, limit=None, lookup_lines=True, capture_locals=False, compact=False, max_group_width=15, max_group_depth=10)

    後のレンダリングのために例外をキャプチャします。 limit、lookup_lines、capture_locals は `StackSummary` class のものです。

    局所変数がキャプチャされたとき、それらはトレースバックに表示されることに注意してください。

  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)

    例外を書式化します。

    chain が `True` でない場合 `__cause__` と `__context__` は書式化されません。

    返り値は文字列のジェネレータで、それぞれ改行で終わりますが、内部に改行を持つものもあります。 `print_exception()` はこのメソッドのラッパで、単にファイルに出力します。

  format_exception_only(*, show_group=False)

    トレースバックの例外部を書式化します。

    返り値は文字列のジェネレータで、それぞれ改行で終わります。

    When show_group is `False`, 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.

    When show_group is `True`, and the exception is an instance of `BaseExceptionGroup`, the nested exceptions are included as well, recursively, with indentation relative to their nesting depth.

    バージョン 3.11 で変更: The exception's `notes` are now included in the output.

    バージョン 3.13 で変更: show_group パラメータが追加されました。

## `StackSummary` オブジェクト

Added in version 3.5.

`StackSummary` オブジェクトは書式化の準備ができているコールスタックを表します。

class traceback.StackSummary
  classmethod extract(frame_gen, *, limit=None, lookup_lines=True, capture_locals=False)

    ジェネレータ (例えば `walk_stack()` や `walk_tb()` が返すもの) から `StackSummary` を構築します。

    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.

    バージョン 3.12 で変更: 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.

    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.

    バージョン 3.6 で変更: Long sequences of repeated frames are now abbreviated.

  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` オブジェクト

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, end_lineno=None, colno=None, end_colno=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 mapping, and if supplied the variable representations are stored in the summary for later display.

  `FrameSummary` インスタンスは以下の属性を持ちます:

  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`.

  end_lineno

    The last line number of the source code for this frame. By default, it is set to `lineno` and indexation starts from 1.

    バージョン 3.13 で変更: The default value changed from `None` to `lineno`.

  colno

    The column number of the source code for this frame. By default, it is `None` and indexation starts from 0.

  end_colno

    The last column number of the source code for this frame. By default, it is `None` and indexation starts from 0.

## Examples of Using the Module-Level Functions

この簡単な例では基本的な read-eval-print ループを実装しています。標準的な Python の対話インタープリタループに似ていますが、 Python のものより便利ではありません。インタープリタループのより完全な実装については、 `code` モジュールを参照してください。

    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)

次の例は例外とトレースバックの出力並びに形式が異なることを示します:

    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)

この例の出力は次のようになります:

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

次の例は、スタックの print と format の違いを示しています:

    >>> 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']

最後の例は、残りの幾つかの関数のデモをします:

    >>> 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