# 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