# `traceback` --- Print or retrieve a stack traceback

ソースコード: Lib/traceback.py

このモジュールは Python プログラムのスタックトレースを抽出し、書式を整え、表示するための標準インターフェースを提供します。モジュールがスタックトレースを表示するとき、Python インタープリタの動作を正確に模倣します。インタープリタの"ラッパー"の場合のように、プログラムの制御の元でスタックトレースを表示したいと思ったときに役に立ちます。

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.

Module `pdb`

  Interactive source code debugger for Python programs.

このモジュールには、以下の関数が定義されています:

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.

  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)

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

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

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

  - 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.

  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.

  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, file, chain)` の省略表現です。

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()`.

  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 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.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])

  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.

  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.

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.

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.

このモジュールは以下のクラスも定義しています:

## `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 in a lightweight fashion.

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)

  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。

  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: 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

    トレースバックを表す `StackSummary`。

  exc_type

    元々のトレースバックのクラス。

  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)

    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。

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

    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()

    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。

    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.

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

## `StackSummary` オブジェクト

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.

    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)

  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`.

## トレースバックの例

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:
        exc = sys.exception()
        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',
     '  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

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