內建的例外
**********

在 Python 中，所有例外必須是從 "BaseException" 衍生的類別的實例。在陳
述式 "try" 搭配 "except" 子句裡提到一個特定的類別時，那個子句也會處理
任何從該類別衍生的例外類別（但不會處理該類別*衍生自*的例外類別）。兩個
不是由子類別關係關聯起來的例外類別永遠不相等，就算它們有相同的名稱也是
如此。

此章節裡列出的內建例外可以從直譯器或內建函式產生。除了特別提到的地方之
外，它們會有一個*關聯值*表示錯誤發生的詳細原因。這可能是一個字串，或者
是一些資訊項目組成的元組（例如一個錯誤代碼及一個解釋該代碼的字串）。這
個關聯值通常當作引數傳遞給例外類別的建構函式。

使用者的程式碼可以引發內建例外。這可以用來測試例外處理器或者用來回報一
個錯誤條件，*就像*直譯器會引發相同例外的情況；但需要注意的是沒有任何方
式可以避免使用者的程式碼引發不適當的錯誤。

可以從內建的例外類別定義新的例外子類別；程式設計師被鼓勵從 "Exception"
類別或其子類別衍生新的例外，而不是從 "BaseException" 來衍生。更多關於
定義例外的資訊可以在 Python 教學中的使用者自定的例外裡取得。


例外的情境
==========

三個例外物件上的屬性提供關於引發此例外的情境的資訊：

BaseException.__context__
BaseException.__cause__
BaseException.__suppress_context__

   當引發一個新的例外而同時有另一個例外已經正在被處理時，這個新例外的
   "__context__" 屬性會自動被設成那個已處理的例外。當使用 "except" 或
   "finally" 子句或 "with" 陳述式的時候例外會被處理。

   這個隱含的例外情境可以透過使用 "from" 搭配 "raise" 來補充明確的原因
   ：

      raise new_exc from original_exc

   在 "from" 後面的運算式必須是一個例外或 "None"。它將會被設定成所引發
   例外的 "__cause__"。設定 "__cause__" 也隱含地設定
   "__suppress_context__" 屬性為 "True"，因此使用 "raise new_exc from
   None" 實際上會以新的例外取代舊的例外以利於顯示（例如轉換 "KeyError"
   為 "AttributeError"），同時保持舊的例外可以透過 "__context__" 取得
   以方便 debug 的時候檢查。

   預設的回溯 (traceback) 顯示程式碼會顯示這些連鎖的例外 (chained
   exception) 加上例外本身的回溯。當存在的時候，在 "__cause__" 中明確
   地連鎖的例外總是會被顯示。而在 "__context__" 中隱含地連鎖的例外只有
   當 "__cause__" 是 "None" 且 "__suppress_context__" 是 false 時才會
   顯示。

   在任一種情況下，例外本身總是會顯示在任何連鎖例外的後面，因此回溯的
   最後一行總是顯示最後一個被引發的例外。


繼承自內建的例外
================

使用者的程式碼可以建立繼承自例外類型的子類別。建議一次只繼承一種例外類
型以避免在基底類別之間如何處理 "args" 屬性的任何可能衝突，以及可能的記
憶體佈局 (memory layout) 不相容。

**CPython 實作細節：** 為了效率，大部分的內建例外使用 C 來實作，參考
Objects/exceptions.c。一些例外有客製化的記憶體佈局，使其不可能建立一個
繼承多種例外類型的子類別。類型的記憶體佈局是實作細節且可能會在不同
Python 版本間改變，造成未來新的衝突。因此，總之建議避免繼承多種例外類
型。


基底類別 (base classes)
=======================

以下的例外大部分被用在當作其他例外的基底類別。

exception BaseException

   所有內建例外的基底類別。這不是為了讓使用者定義的類別直接繼承（可以
   使用 "Exception"）。如果在這個類別的實例上呼叫 "str()"，會回傳實例
   的引數的表示，或者沒有引數的時候會回傳空字串。

   args

      提供給該例外建構函式的引數元組。一些內建的例外（像是 "OSError"）
      預期接受特定數量的引數並賦予該元組的每一個元素一個特別的意義，其
      他例外則通常用一個提供錯誤訊息的單一字串來呼叫。

   with_traceback(tb)

      此方法設定 *tb* 為該例外的新的回溯並回傳該例外物件。在 **PEP
      3134** 的例外連鎖功能變得可用之前，此方法曾被更普遍使用。下面的
      範例顯示我們如何將 "SomeException" 的實例轉換為 "OtherException"
      的實例同時保留回溯。一旦被引發，目前的 frame 會被加進
      "OtherException" 的回溯，就像原來 "SomeException" 的回溯會發生的
      一樣，我們允許它被傳遞給呼叫者：

         try:
             ...
         except SomeException:
             tb = sys.exception().__traceback__
             raise OtherException(...).with_traceback(tb)

   __traceback__

      可寫入的欄位，儲存關聯到該例外的回溯物件。也可以參考 The raise
      statement。

   add_note(note)

      新增字串 "note" 到例外的備註，在標準的回溯裡，備註出現在例外字串
      的後面。如果 "note" 不是字串則引發 "TypeError"。

      在 3.11 版被加入.

   __notes__

      該例外的備註串列，使用 "add_note()" 來新增。此屬性在
      "add_note()" 被呼叫的時候建立。

      在 3.11 版被加入.

exception Exception

   所有內建、非系統退出 (non-system-exiting) 的例外都衍生自此類別。所
   有使用者定義的例外應該也要衍生自此類別。

exception ArithmeticError

   各種運算錯誤所引發的那些內建例外："OverflowError"、
   "ZeroDivisionError"、"FloatingPointError" 的基底類別。

exception BufferError

   當緩衝 (buffer) 相關的操作無法被執行時會引發此例外。

exception LookupError

   當使用在對映或序列上的鍵或索引是無效的時候所引發的例外：
   "IndexError"、"KeyError" 的基底類別。這可以被 "codecs.lookup()" 直
   接引發。


實體例外
========

以下的例外是通常會被引發的例外。

exception AssertionError

   當 "assert" 陳述式失敗的時候被引發。

exception AttributeError

   當屬性參照（參考 Attribute references）或賦值失敗的時候被引發。（當
   物件根本不支援屬性參照或屬性賦值的時候，"TypeError" 會被引發。）

   "name" 和 "obj" 屬性可以使用建構函式的僅限關鍵字 (keyword-only) 引
   數來設定。當被設定的時候，它們分別代表被嘗試存取的屬性名稱以及被以
   該屬性存取的物件。

   在 3.10 版的變更: 新增 "name" 與 "obj" 屬性。

exception EOFError

   當 "input()" 函式在沒有讀到任何資料而到達檔案結尾 (end-of-file,
   EOF) 條件的時候被引發。（注意："io.IOBase.read()" 和
   "io.IOBase.readline()" 方法當達到 EOF 時會回傳空字串。）

exception FloatingPointError

   目前沒有被使用。

exception GeneratorExit

   當 *generator* 或 *coroutine* 被關閉的時候被引發；參考
   "generator.close()" 和 "coroutine.close()"。此例外直接繼承自
   "BaseException" 而不是 "Exception"，因為技術上來說這不是一個錯誤。

exception ImportError

   當 "import" 陳述式嘗試載入模組遇到問題的時候會被引發。當 "from …
   import" 裡的 “from list” 包含找不到的名稱時也會被引發。

   可選的僅限關鍵字引數 *name* 和 *path* 設定對應的屬性：

   name

      嘗試引入 (import) 的模組名稱。

   path

      觸發此例外的任何檔案的路徑。

   在 3.3 版的變更: 新增 "name" 與 "path" 屬性。

exception ModuleNotFoundError

   "ImportError" 的子類別，當模組不能被定位的時候會被 "import" 所引發
   。當在 "sys.modules" 裡找到 "None" 時也會被引發。

   在 3.6 版被加入.

exception IndexError

   當序列的索引超出範圍的時候會被引發。（切片索引 (slice indices) 會默
   默地被截短使其能落在允許的範圍內；如果索引不是整數，"TypeError" 會
   被引發。）

exception KeyError

   當對映（字典）的鍵無法在已存在的鍵的集合中被找到時會被引發。

exception KeyboardInterrupt

   當使用者輸入中斷鍵 (interrupt key)（一般來說是 "Control-C" 或
   "Delete"）時會被引發。在執行過程中，會定期檢查是否產生中斷。此例外
   繼承自 "BaseException" 以防止意外地被捕捉 "Exception" 的程式碼所捕
   捉，而因此讓直譯器無法結束。

   備註:

     捕捉 "KeyboardInterrupt" 需要特殊的考量。因為它可以在無法預期的時
     間點被引發，可能在某些情況下讓正在跑的程式處在一個不一致的狀態。
     一般來說最好讓 "KeyboardInterrupt" 越快結束程式越好，或者完全避免
     引發它。（參考 Note on Signal Handlers and Exceptions。）

exception MemoryError

   當一個操作用光了記憶體但情況還可能被修復 (rescued)（透過刪除一些物
   件）的時候被引發。關聯的值是一個字串，表示什麼類型的（內部）操作用
   光了記憶體。需注意的是因為底層的記憶體管理架構（C 的 "malloc()" 函
   式），直譯器可能無法總是完整地從該情況中修復；僅管如此，它還是引發
   例外以讓堆疊回溯可以被印出，以防原因出在失控的程式。

exception NameError

   當找不到本地或全域的名稱時會被引發。這只應用在不合格的名稱
   (unqualified name) 上。關聯的值是一個錯誤訊息，包含那個無法被找到的
   名稱。

   "name" 屬性可以使用僅限關鍵字引數來設定到建構函式。當被設定的時候它
   代表被嘗試存取的變數名稱。

   在 3.10 版的變更: 新增 "name" 屬性。

exception NotImplementedError

   This exception is derived from "RuntimeError".  In user defined
   base classes, abstract methods should raise this exception when
   they require derived classes to override the method, or while the
   class is being developed to indicate that the real implementation
   still needs to be added.

   備註:

     It should not be used to indicate that an operator or method is
     not meant to be supported at all -- in that case either leave the
     operator / method undefined or, if a subclass, set it to "None".

   備註:

     "NotImplementedError" and "NotImplemented" are not
     interchangeable, even though they have similar names and
     purposes.  See "NotImplemented" for details on when to use it.

exception OSError([arg])
exception OSError(errno, strerror[, filename[, winerror[, filename2]]])

   This exception is raised when a system function returns a system-
   related error, including I/O failures such as "file not found" or
   "disk full" (not for illegal argument types or other incidental
   errors).

   The second form of the constructor sets the corresponding
   attributes, described below.  The attributes default to "None" if
   not specified.  For backwards compatibility, if three arguments are
   passed, the "args" attribute contains only a 2-tuple of the first
   two constructor arguments.

   The constructor often actually returns a subclass of "OSError", as
   described in OS exceptions below.  The particular subclass depends
   on the final "errno" value.  This behaviour only occurs when
   constructing "OSError" directly or via an alias, and is not
   inherited when subclassing.

   errno

      A numeric error code from the C variable "errno".

   winerror

      Under Windows, this gives you the native Windows error code.
      The "errno" attribute is then an approximate translation, in
      POSIX terms, of that native error code.

      Under Windows, if the *winerror* constructor argument is an
      integer, the "errno" attribute is determined from the Windows
      error code, and the *errno* argument is ignored.  On other
      platforms, the *winerror* argument is ignored, and the
      "winerror" attribute does not exist.

   strerror

      The corresponding error message, as provided by the operating
      system.  It is formatted by the C functions "perror()" under
      POSIX, and "FormatMessage()" under Windows.

   filename
   filename2

      For exceptions that involve a file system path (such as "open()"
      or "os.unlink()"), "filename" is the file name passed to the
      function. For functions that involve two file system paths (such
      as "os.rename()"), "filename2" corresponds to the second file
      name passed to the function.

   在 3.3 版的變更: "EnvironmentError", "IOError", "WindowsError",
   "socket.error", "select.error" and "mmap.error" have been merged
   into "OSError", and the constructor may return a subclass.

   在 3.4 版的變更: The "filename" attribute is now the original file
   name passed to the function, instead of the name encoded to or
   decoded from the *filesystem encoding and error handler*. Also, the
   *filename2* constructor argument and attribute was added.

exception OverflowError

   Raised when the result of an arithmetic operation is too large to
   be represented.  This cannot occur for integers (which would rather
   raise "MemoryError" than give up).  However, for historical
   reasons, OverflowError is sometimes raised for integers that are
   outside a required range.   Because of the lack of standardization
   of floating-point exception handling in C, most floating-point
   operations are not checked.

exception RecursionError

   This exception is derived from "RuntimeError".  It is raised when
   the interpreter detects that the maximum recursion depth (see
   "sys.getrecursionlimit()") is exceeded.

   在 3.5 版被加入: Previously, a plain "RuntimeError" was raised.

exception ReferenceError

   This exception is raised when a weak reference proxy, created by
   the "weakref.proxy()" function, is used to access an attribute of
   the referent after it has been garbage collected. For more
   information on weak references, see the "weakref" module.

exception RuntimeError

   Raised when an error is detected that doesn't fall in any of the
   other categories.  The associated value is a string indicating what
   precisely went wrong.

exception StopIteration

   Raised by built-in function "next()" and an *iterator*'s
   "__next__()" method to signal that there are no further items
   produced by the iterator.

   value

      The exception object has a single attribute "value", which is
      given as an argument when constructing the exception, and
      defaults to "None".

   When a *generator* or *coroutine* function returns, a new
   "StopIteration" instance is raised, and the value returned by the
   function is used as the "value" parameter to the constructor of the
   exception.

   If a generator code directly or indirectly raises "StopIteration",
   it is converted into a "RuntimeError" (retaining the
   "StopIteration" as the new exception's cause).

   在 3.3 版的變更: Added "value" attribute and the ability for
   generator functions to use it to return a value.

   在 3.5 版的變更: Introduced the RuntimeError transformation via
   "from __future__ import generator_stop", see **PEP 479**.

   在 3.7 版的變更: Enable **PEP 479** for all code by default: a
   "StopIteration" error raised in a generator is transformed into a
   "RuntimeError".

exception StopAsyncIteration

   Must be raised by "__anext__()" method of an *asynchronous
   iterator* object to stop the iteration.

   在 3.5 版被加入.

exception SyntaxError(message, details)

   Raised when the parser encounters a syntax error.  This may occur
   in an "import" statement, in a call to the built-in functions
   "compile()", "exec()", or "eval()", or when reading the initial
   script or standard input (also interactively).

   The "str()" of the exception instance returns only the error
   message. Details is a tuple whose members are also available as
   separate attributes.

   filename

      The name of the file the syntax error occurred in.

   lineno

      Which line number in the file the error occurred in. This is
      1-indexed: the first line in the file has a "lineno" of 1.

   offset

      The column in the line where the error occurred. This is
      1-indexed: the first character in the line has an "offset" of 1.

   text

      The source code text involved in the error.

   end_lineno

      Which line number in the file the error occurred ends in. This
      is 1-indexed: the first line in the file has a "lineno" of 1.

   end_offset

      The column in the end line where the error occurred finishes.
      This is 1-indexed: the first character in the line has an
      "offset" of 1.

   For errors in f-string fields, the message is prefixed by
   "f-string: " and the offsets are offsets in a text constructed from
   the replacement expression.  For example, compiling f'Bad {a b}
   field' results in this args attribute: ('f-string: ...', ('', 1, 2,
   '(a b)n', 1, 5)).

   在 3.10 版的變更: 新增 "end_lineno" 與 "end_offset" 屬性。

exception IndentationError

   Base class for syntax errors related to incorrect indentation.
   This is a subclass of "SyntaxError".

exception TabError

   Raised when indentation contains an inconsistent use of tabs and
   spaces. This is a subclass of "IndentationError".

exception SystemError

   Raised when the interpreter finds an internal error, but the
   situation does not look so serious to cause it to abandon all hope.
   The associated value is a string indicating what went wrong (in
   low-level terms).

   You should report this to the author or maintainer of your Python
   interpreter. Be sure to report the version of the Python
   interpreter ("sys.version"; it is also printed at the start of an
   interactive Python session), the exact error message (the
   exception's associated value) and if possible the source of the
   program that triggered the error.

exception SystemExit

   This exception is raised by the "sys.exit()" function.  It inherits
   from "BaseException" instead of "Exception" so that it is not
   accidentally caught by code that catches "Exception".  This allows
   the exception to properly propagate up and cause the interpreter to
   exit.  When it is not handled, the Python interpreter exits; no
   stack traceback is printed.  The constructor accepts the same
   optional argument passed to "sys.exit()". If the value is an
   integer, it specifies the system exit status (passed to C's
   "exit()" function); if it is "None", the exit status is zero; if it
   has another type (such as a string), the object's value is printed
   and the exit status is one.

   A call to "sys.exit()" is translated into an exception so that
   clean-up handlers ("finally" clauses of "try" statements) can be
   executed, and so that a debugger can execute a script without
   running the risk of losing control.  The "os._exit()" function can
   be used if it is absolutely positively necessary to exit
   immediately (for example, in the child process after a call to
   "os.fork()").

   code

      The exit status or error message that is passed to the
      constructor. (Defaults to "None".)

exception TypeError

   Raised when an operation or function is applied to an object of
   inappropriate type.  The associated value is a string giving
   details about the type mismatch.

   This exception may be raised by user code to indicate that an
   attempted operation on an object is not supported, and is not meant
   to be. If an object is meant to support a given operation but has
   not yet provided an implementation, "NotImplementedError" is the
   proper exception to raise.

   Passing arguments of the wrong type (e.g. passing a "list" when an
   "int" is expected) should result in a "TypeError", but passing
   arguments with the wrong value (e.g. a number outside expected
   boundaries) should result in a "ValueError".

exception UnboundLocalError

   Raised when a reference is made to a local variable in a function
   or method, but no value has been bound to that variable.  This is a
   subclass of "NameError".

exception UnicodeError

   Raised when a Unicode-related encoding or decoding error occurs.
   It is a subclass of "ValueError".

   "UnicodeError" has attributes that describe the encoding or
   decoding error.  For example, "err.object[err.start:err.end]" gives
   the particular invalid input that the codec failed on.

   encoding

      The name of the encoding that raised the error.

   reason

      A string describing the specific codec error.

   object

      The object the codec was attempting to encode or decode.

   start

      The first index of invalid data in "object".

   end

      The index after the last invalid data in "object".

exception UnicodeEncodeError

   Raised when a Unicode-related error occurs during encoding.  It is
   a subclass of "UnicodeError".

exception UnicodeDecodeError

   Raised when a Unicode-related error occurs during decoding.  It is
   a subclass of "UnicodeError".

exception UnicodeTranslateError

   Raised when a Unicode-related error occurs during translating.  It
   is a subclass of "UnicodeError".

exception ValueError

   Raised when an operation or function receives an argument that has
   the right type but an inappropriate value, and the situation is not
   described by a more precise exception such as "IndexError".

exception ZeroDivisionError

   Raised when the second argument of a division or modulo operation
   is zero.  The associated value is a string indicating the type of
   the operands and the operation.

The following exceptions are kept for compatibility with previous
versions; starting from Python 3.3, they are aliases of "OSError".

exception EnvironmentError

exception IOError

exception WindowsError

   僅限於在 Windows 中使用。


OS exceptions
-------------

The following exceptions are subclasses of "OSError", they get raised
depending on the system error code.

exception BlockingIOError

   Raised when an operation would block on an object (e.g. socket) set
   for non-blocking operation. Corresponds to "errno" "EAGAIN",
   "EALREADY", "EWOULDBLOCK" and "EINPROGRESS".

   In addition to those of "OSError", "BlockingIOError" can have one
   more attribute:

   characters_written

      An integer containing the number of characters written to the
      stream before it blocked.  This attribute is available when
      using the buffered I/O classes from the "io" module.

exception ChildProcessError

   Raised when an operation on a child process failed. Corresponds to
   "errno" "ECHILD".

exception ConnectionError

   A base class for connection-related issues.

   Subclasses are "BrokenPipeError", "ConnectionAbortedError",
   "ConnectionRefusedError" and "ConnectionResetError".

exception BrokenPipeError

   A subclass of "ConnectionError", raised when trying to write on a
   pipe while the other end has been closed, or trying to write on a
   socket which has been shutdown for writing. Corresponds to "errno"
   "EPIPE" and "ESHUTDOWN".

exception ConnectionAbortedError

   A subclass of "ConnectionError", raised when a connection attempt
   is aborted by the peer. Corresponds to "errno" "ECONNABORTED".

exception ConnectionRefusedError

   A subclass of "ConnectionError", raised when a connection attempt
   is refused by the peer. Corresponds to "errno" "ECONNREFUSED".

exception ConnectionResetError

   A subclass of "ConnectionError", raised when a connection is reset
   by the peer. Corresponds to "errno" "ECONNRESET".

exception FileExistsError

   Raised when trying to create a file or directory which already
   exists. Corresponds to "errno" "EEXIST".

exception FileNotFoundError

   Raised when a file or directory is requested but doesn't exist.
   Corresponds to "errno" "ENOENT".

exception InterruptedError

   Raised when a system call is interrupted by an incoming signal.
   Corresponds to "errno" "EINTR".

   在 3.5 版的變更: Python now retries system calls when a syscall is
   interrupted by a signal, except if the signal handler raises an
   exception (see **PEP 475** for the rationale), instead of raising
   "InterruptedError".

exception IsADirectoryError

   Raised when a file operation (such as "os.remove()") is requested
   on a directory. Corresponds to "errno" "EISDIR".

exception NotADirectoryError

   Raised when a directory operation (such as "os.listdir()") is
   requested on something which is not a directory.  On most POSIX
   platforms, it may also be raised if an operation attempts to open
   or traverse a non-directory file as if it were a directory.
   Corresponds to "errno" "ENOTDIR".

exception PermissionError

   Raised when trying to run an operation without the adequate access
   rights - for example filesystem permissions. Corresponds to "errno"
   "EACCES", "EPERM", and "ENOTCAPABLE".

   在 3.11.1 版的變更: WASI's "ENOTCAPABLE" is now mapped to
   "PermissionError".

exception ProcessLookupError

   Raised when a given process doesn't exist. Corresponds to "errno"
   "ESRCH".

exception TimeoutError

   Raised when a system function timed out at the system level.
   Corresponds to "errno" "ETIMEDOUT".

在 3.3 版被加入: All the above "OSError" subclasses were added.

也參考: **PEP 3151** - Reworking the OS and IO exception hierarchy


警告
====

The following exceptions are used as warning categories; see the
Warning Categories documentation for more details.

exception Warning

   Base class for warning categories.

exception UserWarning

   Base class for warnings generated by user code.

exception DeprecationWarning

   Base class for warnings about deprecated features when those
   warnings are intended for other Python developers.

   Ignored by the default warning filters, except in the "__main__"
   module (**PEP 565**). Enabling the Python Development Mode shows
   this warning.

   The deprecation policy is described in **PEP 387**.

exception PendingDeprecationWarning

   Base class for warnings about features which are obsolete and
   expected to be deprecated in the future, but are not deprecated at
   the moment.

   This class is rarely used as emitting a warning about a possible
   upcoming deprecation is unusual, and "DeprecationWarning" is
   preferred for already active deprecations.

   Ignored by the default warning filters. Enabling the Python
   Development Mode shows this warning.

   The deprecation policy is described in **PEP 387**.

exception SyntaxWarning

   Base class for warnings about dubious syntax.

exception RuntimeWarning

   Base class for warnings about dubious runtime behavior.

exception FutureWarning

   Base class for warnings about deprecated features when those
   warnings are intended for end users of applications that are
   written in Python.

exception ImportWarning

   Base class for warnings about probable mistakes in module imports.

   Ignored by the default warning filters. Enabling the Python
   Development Mode shows this warning.

exception UnicodeWarning

   Base class for warnings related to Unicode.

exception EncodingWarning

   Base class for warnings related to encodings.

   細節請見 選擇性加入的編碼警告。

   在 3.10 版被加入.

exception BytesWarning

   Base class for warnings related to "bytes" and "bytearray".

exception ResourceWarning

   Base class for warnings related to resource usage.

   Ignored by the default warning filters. Enabling the Python
   Development Mode shows this warning.

   在 3.2 版被加入.


Exception groups
================

The following are used when it is necessary to raise multiple
unrelated exceptions. They are part of the exception hierarchy so they
can be handled with "except" like all other exceptions. In addition,
they are recognised by "except*", which matches their subgroups based
on the types of the contained exceptions.

exception ExceptionGroup(msg, excs)

exception BaseExceptionGroup(msg, excs)

   Both of these exception types wrap the exceptions in the sequence
   "excs". The "msg" parameter must be a string. The difference
   between the two classes is that "BaseExceptionGroup" extends
   "BaseException" and it can wrap any exception, while
   "ExceptionGroup" extends "Exception" and it can only wrap
   subclasses of "Exception". This design is so that "except
   Exception" catches an "ExceptionGroup" but not
   "BaseExceptionGroup".

   The "BaseExceptionGroup" constructor returns an "ExceptionGroup"
   rather than a "BaseExceptionGroup" if all contained exceptions are
   "Exception" instances, so it can be used to make the selection
   automatic. The "ExceptionGroup" constructor, on the other hand,
   raises a "TypeError" if any contained exception is not an
   "Exception" subclass.

   message

      The "msg" argument to the constructor. This is a read-only
      attribute.

   exceptions

      A tuple of the exceptions in the "excs" sequence given to the
      constructor. This is a read-only attribute.

   subgroup(condition)

      Returns an exception group that contains only the exceptions
      from the current group that match *condition*, or "None" if the
      result is empty.

      The condition can be either a function that accepts an exception
      and returns true for those that should be in the subgroup, or it
      can be an exception type or a tuple of exception types, which is
      used to check for a match using the same check that is used in
      an "except" clause.

      The nesting structure of the current exception is preserved in
      the result, as are the values of its "message", "__traceback__",
      "__cause__", "__context__" and "__notes__" fields. Empty nested
      groups are omitted from the result.

      The condition is checked for all exceptions in the nested
      exception group, including the top-level and any nested
      exception groups. If the condition is true for such an exception
      group, it is included in the result in full.

   split(condition)

      Like "subgroup()", but returns the pair "(match, rest)" where
      "match" is "subgroup(condition)" and "rest" is the remaining
      non-matching part.

   derive(excs)

      Returns an exception group with the same "message", but which
      wraps the exceptions in "excs".

      This method is used by "subgroup()" and "split()", which are
      used in various contexts to break up an exception group. A
      subclass needs to override it in order to make "subgroup()" and
      "split()" return instances of the subclass rather than
      "ExceptionGroup".

      "subgroup()" and "split()" copy the "__traceback__",
      "__cause__", "__context__" and "__notes__" fields from the
      original exception group to the one returned by "derive()", so
      these fields do not need to be updated by "derive()".

         >>> class MyGroup(ExceptionGroup):
         ...     def derive(self, excs):
         ...         return MyGroup(self.message, excs)
         ...
         >>> e = MyGroup("eg", [ValueError(1), TypeError(2)])
         >>> e.add_note("a note")
         >>> e.__context__ = Exception("context")
         >>> e.__cause__ = Exception("cause")
         >>> try:
         ...    raise e
         ... except Exception as e:
         ...    exc = e
         ...
         >>> match, rest = exc.split(ValueError)
         >>> exc, exc.__context__, exc.__cause__, exc.__notes__
         (MyGroup('eg', [ValueError(1), TypeError(2)]), Exception('context'), Exception('cause'), ['a note'])
         >>> match, match.__context__, match.__cause__, match.__notes__
         (MyGroup('eg', [ValueError(1)]), Exception('context'), Exception('cause'), ['a note'])
         >>> rest, rest.__context__, rest.__cause__, rest.__notes__
         (MyGroup('eg', [TypeError(2)]), Exception('context'), Exception('cause'), ['a note'])
         >>> exc.__traceback__ is match.__traceback__ is rest.__traceback__
         True

   Note that "BaseExceptionGroup" defines "__new__()", so subclasses
   that need a different constructor signature need to override that
   rather than "__init__()". For example, the following defines an
   exception group subclass which accepts an exit_code and and
   constructs the group's message from it.

      class Errors(ExceptionGroup):
         def __new__(cls, errors, exit_code):
            self = super().__new__(Errors, f"exit code: {exit_code}", errors)
            self.exit_code = exit_code
            return self

         def derive(self, excs):
            return Errors(excs, self.exit_code)

   Like "ExceptionGroup", any subclass of "BaseExceptionGroup" which
   is also a subclass of "Exception" can only wrap instances of
   "Exception".

   在 3.11 版被加入.


例外階層
========

內建例外的類別階層如下：

   BaseException
    ├── BaseExceptionGroup
    ├── GeneratorExit
    ├── KeyboardInterrupt
    ├── SystemExit
    └── Exception
         ├── ArithmeticError
         │    ├── FloatingPointError
         │    ├── OverflowError
         │    └── ZeroDivisionError
         ├── AssertionError
         ├── AttributeError
         ├── BufferError
         ├── EOFError
         ├── ExceptionGroup [BaseExceptionGroup]
         ├── ImportError
         │    └── ModuleNotFoundError
         ├── LookupError
         │    ├── IndexError
         │    └── KeyError
         ├── MemoryError
         ├── NameError
         │    └── UnboundLocalError
         ├── OSError
         │    ├── BlockingIOError
         │    ├── ChildProcessError
         │    ├── ConnectionError
         │    │    ├── BrokenPipeError
         │    │    ├── ConnectionAbortedError
         │    │    ├── ConnectionRefusedError
         │    │    └── ConnectionResetError
         │    ├── FileExistsError
         │    ├── FileNotFoundError
         │    ├── InterruptedError
         │    ├── IsADirectoryError
         │    ├── NotADirectoryError
         │    ├── PermissionError
         │    ├── ProcessLookupError
         │    └── TimeoutError
         ├── ReferenceError
         ├── RuntimeError
         │    ├── NotImplementedError
         │    └── RecursionError
         ├── StopAsyncIteration
         ├── StopIteration
         ├── SyntaxError
         │    └── IndentationError
         │         └── TabError
         ├── SystemError
         ├── TypeError
         ├── ValueError
         │    └── UnicodeError
         │         ├── UnicodeDecodeError
         │         ├── UnicodeEncodeError
         │         └── UnicodeTranslateError
         └── Warning
              ├── BytesWarning
              ├── DeprecationWarning
              ├── EncodingWarning
              ├── FutureWarning
              ├── ImportWarning
              ├── PendingDeprecationWarning
              ├── ResourceWarning
              ├── RuntimeWarning
              ├── SyntaxWarning
              ├── UnicodeWarning
              └── UserWarning
