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[3.10] bpo-25381: Update explanation of exceptions in C. (GH-26838) #29568

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Nov 15, 2021
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[3.10] bpo-25381: Update explanation of exceptions in C. (GH-26838) #29568

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12 changes: 5 additions & 7 deletions Doc/extending/extending.rst
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Expand Up @@ -127,13 +127,11 @@ Intermezzo: Errors and Exceptions

An important convention throughout the Python interpreter is the following: when
a function fails, it should set an exception condition and return an error value
(usually a ``NULL`` pointer). Exceptions are stored in a static global variable
inside the interpreter; if this variable is ``NULL`` no exception has occurred. A
second global variable stores the "associated value" of the exception (the
second argument to :keyword:`raise`). A third variable contains the stack
traceback in case the error originated in Python code. These three variables
are the C equivalents of the result in Python of :meth:`sys.exc_info` (see the
section on module :mod:`sys` in the Python Library Reference). It is important
(usually ``-1`` or a ``NULL`` pointer). Exception information is stored in
three members of the interpreter's thread state. These are ``NULL`` if
there is no exception. Otherwise they are the C equivalents of the members
of the Python tuple returned by :meth:`sys.exc_info`. These are the
exception type, exception instance, and a traceback object. It is important
to know about them to understand how errors are passed around.

The Python API defines a number of functions to set various types of exceptions.
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Documentation/2021-06-21-17-51-51.bpo-25381.7Kn-_H.rst
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@@ -0,0 +1,2 @@
In the extending chapter of the extending doc, update a paragraph about the
global variables containing exception information.