The functions described in this chapter will let you handle and raise Python
exceptions. It is important to understand some of the basics of Python
exception handling. It works somewhat like the POSIX errno variable:
there is a global indicator (per thread) of the last error that occurred. Most
C API functions don't clear this on success, but will set it to indicate the
cause of the error on failure. Most C API functions also return an error
indicator, usually NULL if they are supposed to return a pointer, or -1
if they return an integer (exception: the PyArg_* functions
return 1 for success and 0 for failure).
Concretely, the error indicator consists of three object pointers: the
exception's type, the exception's value, and the traceback object. Any
of those pointers can be NULL if non-set (although some combinations are
forbidden, for example you can't have a non-NULL traceback if the exception
type is NULL).
When a function must fail because some function it called failed, it generally doesn't set the error indicator; the function it called already set it. It is responsible for either handling the error and clearing the exception or returning after cleaning up any resources it holds (such as object references or memory allocations); it should not continue normally if it is not prepared to handle the error. If returning due to an error, it is important to indicate to the caller that an error has been set. If the error is not handled or carefully propagated, additional calls into the Python/C API may not behave as intended and may fail in mysterious ways.
備註
The error indicator is not the result of sys.exc_info().
The former corresponds to an exception that is not yet caught (and is
therefore still propagating), while the latter returns an exception after
it is caught (and has therefore stopped propagating).
Clear the error indicator. If the error indicator is not set, there is no effect.
Print a standard traceback to sys.stderr and clear the error indicator.
Unless the error is a SystemExit, in that case no traceback is
printed and the Python process will exit with the error code specified by
the SystemExit instance.
Call this function only when the error indicator is set. Otherwise it will cause a fatal error!
If set_sys_last_vars is nonzero, the variable sys.last_exc is
set to the printed exception. For backwards compatibility, the
deprecated variables sys.last_type, sys.last_value and
sys.last_traceback are also set to the type, value and traceback
of this exception, respectively.
在 3.12 版的變更: The setting of sys.last_exc was added.
PyErr_PrintEx(1) 的別名。
Call sys.unraisablehook() using the current exception and obj
argument.
This utility function prints a warning message to sys.stderr when an
exception has been set but it is impossible for the interpreter to actually
raise the exception. It is used, for example, when an exception occurs in an
__del__() method.
The function is called with a single argument obj that identifies the context
in which the unraisable exception occurred. If possible,
the repr of obj will be printed in the warning message.
If obj is NULL, only the traceback is printed.
An exception must be set when calling this function.
在 3.4 版的變更: Print a traceback. Print only traceback if obj is NULL.
在 3.8 版的變更: 使用 sys.unraisablehook()。
Similar to PyErr_WriteUnraisable(), but the format and subsequent
parameters help format the warning message; they have the same meaning and
values as in PyUnicode_FromFormat().
PyErr_WriteUnraisable(obj) is roughly equivalent to
PyErr_FormatUnraisable("Exception ignored in: %R", obj).
If format is NULL, only the traceback is printed.
在 3.13 版被加入.
Print the standard traceback display of exc to sys.stderr, including
chained exceptions and notes.
在 3.12 版被加入.
These functions help you set the current thread's error indicator.
For convenience, some of these functions will always return a
NULL pointer for use in a return statement.
This is the most common way to set the error indicator. The first argument
specifies the exception type; it is normally one of the standard exceptions,
e.g. PyExc_RuntimeError. You need not create a new
strong reference to it (e.g. with Py_INCREF()).
The second argument is an error message; it is decoded from 'utf-8'.
This function is similar to PyErr_SetString() but lets you specify an
arbitrary Python object for the "value" of the exception.
This function sets the error indicator and returns NULL. exception
should be a Python exception class. The format and subsequent
parameters help format the error message; they have the same meaning and
values as in PyUnicode_FromFormat(). format is an ASCII-encoded
string.
Same as PyErr_Format(), but taking a va_list argument rather
than a variable number of arguments.
在 3.5 版被加入.
This is a shorthand for PyErr_SetObject(type, Py_None).
This is a shorthand for PyErr_SetString(PyExc_TypeError, message), where
message indicates that a built-in operation was invoked with an illegal
argument. It is mostly for internal use.
This is a shorthand for PyErr_SetNone(PyExc_MemoryError); it returns NULL
so an object allocation function can write return PyErr_NoMemory(); when it
runs out of memory.
This is a convenience function to raise an exception when a C library function
has returned an error and set the C variable errno. It constructs a
tuple object whose first item is the integer errno value and whose
second item is the corresponding error message (gotten from strerror()),
and then calls PyErr_SetObject(type, object). On Unix, when the
errno value is EINTR, indicating an interrupted system call,
this calls PyErr_CheckSignals(), and if that set the error indicator,
leaves it set to that. The function always returns NULL, so a wrapper
function around a system call can write return PyErr_SetFromErrno(type);
when the system call returns an error.
Similar to PyErr_SetFromErrno(), with the additional behavior that if
filenameObject is not NULL, it is passed to the constructor of type as
a third parameter. In the case of OSError exception,
this is used to define the filename attribute of the
exception instance.
Similar to PyErr_SetFromErrnoWithFilenameObject(), but takes a second
filename object, for raising errors when a function that takes two filenames
fails.
在 3.4 版被加入.
Similar to PyErr_SetFromErrnoWithFilenameObject(), but the filename
is given as a C string. filename is decoded from the filesystem
encoding and error handler.
This is a convenience function to raise OSError. If called with
ierr of 0, the error code returned by a call to GetLastError()
is used instead. It calls the Win32 function FormatMessage() to retrieve
the Windows description of error code given by ierr or GetLastError(),
then it constructs a OSError object with the winerror
attribute set to the error code, the strerror attribute
set to the corresponding error message (gotten from
FormatMessage()), and then calls PyErr_SetObject(PyExc_OSError,
object). This function always returns NULL.
適用: Windows.
Similar to PyErr_SetFromWindowsErr(), with an additional parameter
specifying the exception type to be raised.
適用: Windows.
Similar to PyErr_SetFromWindowsErr(), with the additional behavior
that if filename is not NULL, it is decoded from the filesystem
encoding (os.fsdecode()) and passed to the constructor of
OSError as a third parameter to be used to define the
filename attribute of the exception instance.
適用: Windows.
Similar to PyErr_SetExcFromWindowsErr(), with the additional behavior
that if filename is not NULL, it is passed to the constructor of
OSError as a third parameter to be used to define the
filename attribute of the exception instance.
適用: Windows.
Similar to PyErr_SetExcFromWindowsErrWithFilenameObject(),
but accepts a second filename object.
適用: Windows.
在 3.4 版被加入.
Similar to PyErr_SetFromWindowsErrWithFilename(), with an additional
parameter specifying the exception type to be raised.
適用: Windows.
This is a convenience function to raise ImportError. msg will be
set as the exception's message string. name and path, both of which can
be NULL, will be set as the ImportError's respective name
and path attributes.
在 3.3 版被加入.
Much like PyErr_SetImportError() but this function allows for
specifying a subclass of ImportError to raise.
在 3.6 版被加入.
Set file, line, and offset information for the current exception. If the
current exception is not a SyntaxError, then it sets additional
attributes, which make the exception printing subsystem think the exception
is a SyntaxError.
在 3.4 版被加入.
Like PyErr_SyntaxLocationObject(), but filename is a byte string
decoded from the filesystem encoding and error handler.
在 3.2 版被加入.
Like PyErr_SyntaxLocationEx(), but the col_offset parameter is
omitted.
This is a shorthand for PyErr_SetString(PyExc_SystemError, message),
where message indicates that an internal operation (e.g. a Python/C API
function) was invoked with an illegal argument. It is mostly for internal
use.
Use these functions to issue warnings from C code. They mirror similar
functions exported by the Python warnings module. They normally
print a warning message to sys.stderr; however, it is
also possible that the user has specified that warnings are to be turned into
errors, and in that case they will raise an exception. It is also possible that
the functions raise an exception because of a problem with the warning machinery.
The return value is 0 if no exception is raised, or -1 if an exception
is raised. (It is not possible to determine whether a warning message is
actually printed, nor what the reason is for the exception; this is
intentional.) If an exception is raised, the caller should do its normal
exception handling (for example, Py_DECREF() owned references and return
an error value).
Issue a warning message. The category argument is a warning category (see
below) or NULL; the message argument is a UTF-8 encoded string. stack_level is a
positive number giving a number of stack frames; the warning will be issued from
the currently executing line of code in that stack frame. A stack_level of 1
is the function calling PyErr_WarnEx(), 2 is the function above that,
and so forth.
Warning categories must be subclasses of PyExc_Warning;
PyExc_Warning is a subclass of PyExc_Exception;
the default warning category is PyExc_RuntimeWarning. The standard
Python warning categories are available as global variables whose names are
enumerated at Standard Warning Categories.
For information about warning control, see the documentation for the
warnings module and the -W option in the command line
documentation. There is no C API for warning control.
Issue a warning message with explicit control over all warning attributes. This
is a straightforward wrapper around the Python function
warnings.warn_explicit(); see there for more information. The module
and registry arguments may be set to NULL to get the default effect
described there.
在 3.4 版被加入.
Similar to PyErr_WarnExplicitObject() except that message and
module are UTF-8 encoded strings, and filename is decoded from the
filesystem encoding and error handler.
Function similar to PyErr_WarnEx(), but use
PyUnicode_FromFormat() to format the warning message. format is
an ASCII-encoded string.
在 3.2 版被加入.
Function similar to PyErr_WarnFormat(), but category is
ResourceWarning and it passes source to warnings.WarningMessage.
在 3.6 版被加入.
Test whether the error indicator is set. If set, return the exception type
(the first argument to the last call to one of the PyErr_Set*
functions or to PyErr_Restore()). If not set, return NULL. You do not
own a reference to the return value, so you do not need to Py_DECREF()
it.
The caller must hold the GIL.
備註
Do not compare the return value to a specific exception; use
PyErr_ExceptionMatches() instead, shown below. (The comparison could
easily fail since the exception may be an instance instead of a class, in the
case of a class exception, or it may be a subclass of the expected exception.)
Equivalent to PyErr_GivenExceptionMatches(PyErr_Occurred(), exc). This
should only be called when an exception is actually set; a memory access
violation will occur if no exception has been raised.
Return true if the given exception matches the exception type in exc. If exc is a class object, this also returns true when given is an instance of a subclass. If exc is a tuple, all exception types in the tuple (and recursively in subtuples) are searched for a match.
Return the exception currently being raised, clearing the error indicator at
the same time. Return NULL if the error indicator is not set.
This function is used by code that needs to catch exceptions, or code that needs to save and restore the error indicator temporarily.
舉例來說：
{
PyObject *exc = PyErr_GetRaisedException();
/* ... code that might produce other errors ... */
PyErr_SetRaisedException(exc);
}
也參考
PyErr_GetHandledException(),
to save the exception currently being handled.
在 3.12 版被加入.
Set exc as the exception currently being raised, clearing the existing exception if one is set.
警告
This call steals a reference to exc, which must be a valid exception.
在 3.12 版被加入.
在 3.12 版之後被棄用: Use PyErr_GetRaisedException() instead.
Retrieve the error indicator into three variables whose addresses are passed.
If the error indicator is not set, set all three variables to NULL. If it is
set, it will be cleared and you own a reference to each object retrieved. The
value and traceback object may be NULL even when the type object is not.
備註
This function is normally only used by legacy code that needs to catch exceptions or save and restore the error indicator temporarily.
舉例來說：
{
PyObject *type, *value, *traceback;
PyErr_Fetch(&type, &value, &traceback);
/* ... code that might produce other errors ... */
PyErr_Restore(type, value, traceback);
}
在 3.12 版之後被棄用: Use PyErr_SetRaisedException() instead.
Set the error indicator from the three objects,
type, value, and traceback,
clearing the existing exception if one is set.
If the objects are NULL, the error
indicator is cleared. Do not pass a NULL type and non-NULL value or
traceback. The exception type should be a class. Do not pass an invalid
exception type or value. (Violating these rules will cause subtle problems
later.) This call takes away a reference to each object: you must own a
reference to each object before the call and after the call you no longer own
these references. (If you don't understand this, don't use this function. I
warned you.)
備註
This function is normally only used by legacy code that needs to
save and restore the error indicator temporarily.
Use PyErr_Fetch() to save the current error indicator.
在 3.12 版之後被棄用: Use PyErr_GetRaisedException() instead,
to avoid any possible de-normalization.
Under certain circumstances, the values returned by PyErr_Fetch() below
can be "unnormalized", meaning that *exc is a class object but *val is
not an instance of the same class. This function can be used to instantiate
the class in that case. If the values are already normalized, nothing happens.
The delayed normalization is implemented to improve performance.
備註
This function does not implicitly set the
__traceback__
attribute on the exception value. If setting the traceback
appropriately is desired, the following additional snippet is needed:
if (tb != NULL) {
PyException_SetTraceback(val, tb);
}
Retrieve the active exception instance, as would be returned by sys.exception().
This refers to an exception that was already caught, not to an exception that was
freshly raised. Returns a new reference to the exception or NULL.
Does not modify the interpreter's exception state.
備註
This function is not normally used by code that wants to handle exceptions.
Rather, it can be used when code needs to save and restore the exception
state temporarily. Use PyErr_SetHandledException() to restore or
clear the exception state.
在 3.11 版被加入.
Set the active exception, as known from sys.exception(). This refers
to an exception that was already caught, not to an exception that was
freshly raised.
To clear the exception state, pass NULL.
備註
This function is not normally used by code that wants to handle exceptions.
Rather, it can be used when code needs to save and restore the exception
state temporarily. Use PyErr_GetHandledException() to get the exception
state.
在 3.11 版被加入.
Retrieve the old-style representation of the exception info, as known from
sys.exc_info(). This refers to an exception that was already caught,
not to an exception that was freshly raised. Returns new references for the
three objects, any of which may be NULL. Does not modify the exception
info state. This function is kept for backwards compatibility. Prefer using
PyErr_GetHandledException().
備註
This function is not normally used by code that wants to handle exceptions.
Rather, it can be used when code needs to save and restore the exception
state temporarily. Use PyErr_SetExcInfo() to restore or clear the
exception state.
在 3.3 版被加入.
Set the exception info, as known from sys.exc_info(). This refers
to an exception that was already caught, not to an exception that was
freshly raised. This function steals the references of the arguments.
To clear the exception state, pass NULL for all three arguments.
This function is kept for backwards compatibility. Prefer using
PyErr_SetHandledException().
備註
This function is not normally used by code that wants to handle exceptions.
Rather, it can be used when code needs to save and restore the exception
state temporarily. Use PyErr_GetExcInfo() to read the exception
state.
在 3.3 版被加入.
在 3.11 版的變更: The type and traceback arguments are no longer used and
can be NULL. The interpreter now derives them from the exception
instance (the value argument). The function still steals
references of all three arguments.
This function interacts with Python's signal handling.
If the function is called from the main thread and under the main Python
interpreter, it checks whether a signal has been sent to the processes
and if so, invokes the corresponding signal handler. If the signal
module is supported, this can invoke a signal handler written in Python.
The function attempts to handle all pending signals, and then returns 0.
However, if a Python signal handler raises an exception, the error
indicator is set and the function returns -1 immediately (such that
other pending signals may not have been handled yet: they will be on the
next PyErr_CheckSignals() invocation).
If the function is called from a non-main thread, or under a non-main
Python interpreter, it does nothing and returns 0.
This function can be called by long-running C code that wants to be interruptible by user requests (such as by pressing Ctrl-C).
備註
The default Python signal handler for SIGINT raises the
KeyboardInterrupt exception.
Simulate the effect of a SIGINT signal arriving.
This is equivalent to PyErr_SetInterruptEx(SIGINT).
備註
This function is async-signal-safe. It can be called without the GIL and from a C signal handler.
Simulate the effect of a signal arriving. The next time
PyErr_CheckSignals() is called, the Python signal handler for
the given signal number will be called.
This function can be called by C code that sets up its own signal handling and wants Python signal handlers to be invoked as expected when an interruption is requested (for example when the user presses Ctrl-C to interrupt an operation).
If the given signal isn't handled by Python (it was set to
signal.SIG_DFL or signal.SIG_IGN), it will be ignored.
If signum is outside of the allowed range of signal numbers, -1
is returned. Otherwise, 0 is returned. The error indicator is
never changed by this function.
備註
This function is async-signal-safe. It can be called without the GIL and from a C signal handler.
在 3.10 版被加入.
This utility function specifies a file descriptor to which the signal number is written as a single byte whenever a signal is received. fd must be non-blocking. It returns the previous such file descriptor.
The value -1 disables the feature; this is the initial state.
This is equivalent to signal.set_wakeup_fd() in Python, but without any
error checking. fd should be a valid file descriptor. The function should
only be called from the main thread.
在 3.5 版的變更: On Windows, the function now also supports socket handles.
This utility function creates and returns a new exception class. The name
argument must be the name of the new exception, a C string of the form
module.classname. The base and dict arguments are normally NULL.
This creates a class object derived from Exception (accessible in C as
PyExc_Exception).
The __module__ attribute of the new class is set to the first part (up
to the last dot) of the name argument, and the class name is set to the last
part (after the last dot). The base argument can be used to specify alternate
base classes; it can either be only one class or a tuple of classes. The dict
argument can be used to specify a dictionary of class variables and methods.
Same as PyErr_NewException(), except that the new exception class can
easily be given a docstring: If doc is non-NULL, it will be used as the
docstring for the exception class.
在 3.2 版被加入.
Return the traceback associated with the exception as a new reference, as
accessible from Python through the __traceback__
attribute. If there is no
traceback associated, this returns NULL.
Set the traceback associated with the exception to tb. Use Py_None to
clear it.
Return the context (another exception instance during whose handling ex was
raised) associated with the exception as a new reference, as accessible from
Python through the __context__ attribute.
If there is no context associated, this returns NULL.
Set the context associated with the exception to ctx. Use NULL to clear
it. There is no type check to make sure that ctx is an exception instance.
This steals a reference to ctx.
Return the cause (either an exception instance, or None,
set by raise ... from ...) associated with the exception as a new
reference, as accessible from Python through the
__cause__ attribute.
Set the cause associated with the exception to cause. Use NULL to clear
it. There is no type check to make sure that cause is either an exception
instance or None. This steals a reference to cause.
The __suppress_context__ attribute is implicitly set
to True by this function.
Return args of exception ex.
Set args of exception ex to args.
Implement part of the interpreter's implementation of except*.
orig is the original exception that was caught, and excs is the list of
the exceptions that need to be raised. This list contains the unhandled
part of orig, if any, as well as the exceptions that were raised from the
except* clauses (so they have a different traceback from orig) and
those that were reraised (and have the same traceback as orig).
Return the ExceptionGroup that needs to be reraised in the end, or
None if there is nothing to reraise.
在 3.12 版被加入.
The following functions are used to create and modify Unicode exceptions from C.
Create a UnicodeDecodeError object with the attributes encoding,
object, length, start, end and reason. encoding and reason are
UTF-8 encoded strings.
Return the encoding attribute of the given exception object.
Return the object attribute of the given exception object.
Get the start attribute of the given exception object and place it into
*start. start must not be NULL. Return 0 on success, -1 on
failure.
Set the start attribute of the given exception object to start. Return
0 on success, -1 on failure.
Get the end attribute of the given exception object and place it into
*end. end must not be NULL. Return 0 on success, -1 on
failure.
Set the end attribute of the given exception object to end. Return 0
on success, -1 on failure.
Return the reason attribute of the given exception object.
Set the reason attribute of the given exception object to reason. Return
0 on success, -1 on failure.
These two functions provide a way to perform safe recursive calls at the C level, both in the core and in extension modules. They are needed if the recursive code does not necessarily invoke Python code (which tracks its recursion depth automatically). They are also not needed for tp_call implementations because the call protocol takes care of recursion handling.
Marks a point where a recursive C-level call is about to be performed.
If USE_STACKCHECK is defined, this function checks if the OS
stack overflowed using PyOS_CheckStack(). If this is the case, it
sets a MemoryError and returns a nonzero value.
The function then checks if the recursion limit is reached. If this is the
case, a RecursionError is set and a nonzero value is returned.
Otherwise, zero is returned.
where should be a UTF-8 encoded string such as " in instance check" to
be concatenated to the RecursionError message caused by the recursion
depth limit.
在 3.9 版的變更: This function is now also available in the limited API.
Ends a Py_EnterRecursiveCall(). Must be called once for each
successful invocation of Py_EnterRecursiveCall().
在 3.9 版的變更: This function is now also available in the limited API.
Properly implementing tp_repr for container types requires
special recursion handling. In addition to protecting the stack,
tp_repr also needs to track objects to prevent cycles. The
following two functions facilitate this functionality. Effectively,
these are the C equivalent to reprlib.recursive_repr().
Called at the beginning of the tp_repr implementation to
detect cycles.
If the object has already been processed, the function returns a
positive integer. In that case the tp_repr implementation
should return a string object indicating a cycle. As examples,
dict objects return {...} and list objects
return [...].
The function will return a negative integer if the recursion limit
is reached. In that case the tp_repr implementation should
typically return NULL.
Otherwise, the function returns zero and the tp_repr
implementation can continue normally.
Ends a Py_ReprEnter(). Must be called once for each
invocation of Py_ReprEnter() that returns zero.
All standard Python exceptions are available as global variables whose names are
PyExc_ followed by the Python exception name. These have the type
PyObject*; they are all class objects. For completeness, here are all
the variables:
C 名稱 |
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在 3.3 版被加入: PyExc_BlockingIOError, PyExc_BrokenPipeError, PyExc_ChildProcessError, PyExc_ConnectionError, PyExc_ConnectionAbortedError, PyExc_ConnectionRefusedError, PyExc_ConnectionResetError, PyExc_FileExistsError, PyExc_FileNotFoundError, PyExc_InterruptedError, PyExc_IsADirectoryError, PyExc_NotADirectoryError, PyExc_PermissionError, PyExc_ProcessLookupError 和 PyExc_TimeoutError 是在 PEP 3151 被引入。
在 3.5 版被加入: PyExc_StopAsyncIteration 和 PyExc_RecursionError。
在 3.6 版被加入: PyExc_ModuleNotFoundError。
These are compatibility aliases to PyExc_OSError:
C 名稱 |
註解 |
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在 3.3 版的變更: These aliases used to be separate exception types.
註解：
All standard Python warning categories are available as global variables whose
names are PyExc_ followed by the Python exception name. These have the type
PyObject*; they are all class objects. For completeness, here are all
the variables:
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Python 名稱 |
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在 3.2 版被加入: PyExc_ResourceWarning.
註解：