"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.

  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.


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)

   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.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])

   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.


"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: 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".


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',
    '  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(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
