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Diffstat (limited to 'Doc/whatsnew/3.3.rst')
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diff --git a/Doc/whatsnew/3.3.rst b/Doc/whatsnew/3.3.rst index 560331f..9023dfa 100644 --- a/Doc/whatsnew/3.3.rst +++ b/Doc/whatsnew/3.3.rst @@ -254,6 +254,9 @@ inspection of exception attributes:: PEP 380: Syntax for Delegating to a Subgenerator ================================================ +:pep:`380` - Syntax for Delegating to a Subgenerator + PEP written by Greg Ewing. + PEP 380 adds the ``yield from`` expression, allowing a generator to delegate part of its operations to another generator. This allows a section of code containing 'yield' to be factored out and placed in another generator. @@ -267,6 +270,67 @@ Kelly and Nick Coghlan, documentation by Zbigniew Jędrzejewski-Szmek and Nick Coghlan) +PEP 409: Suppressing exception context +====================================== + +:pep:`409` - Suppressing exception context + PEP written by Ethan Furman, implemented by Ethan Furman and Nick Coghlan. + +PEP 409 introduces new syntax that allows the display of the chained +exception context to be disabled. This allows cleaner error messages in +applications that convert between exception types:: + + >>> class D: + ... def __init__(self, extra): + ... self._extra_attributes = extra + ... def __getattr__(self, attr): + ... try: + ... return self._extra_attributes[attr] + ... except KeyError: + ... raise AttributeError(attr) from None + ... + >>> D({}).x + Traceback (most recent call last): + File "<stdin>", line 1, in <module> + File "<stdin>", line 8, in __getattr__ + AttributeError: x + +Without the ``from None`` suffix to suppress the cause, the original +exception would be displayed by default:: + + >>> class C: + ... def __init__(self, extra): + ... self._extra_attributes = extra + ... def __getattr__(self, attr): + ... try: + ... return self._extra_attributes[attr] + ... except KeyError: + ... raise AttributeError(attr) + ... + >>> C({}).x + Traceback (most recent call last): + File "<stdin>", line 6, in __getattr__ + KeyError: 'x' + + During handling of the above exception, another exception occurred: + + Traceback (most recent call last): + File "<stdin>", line 1, in <module> + File "<stdin>", line 8, in __getattr__ + AttributeError: x + +No debugging capability is lost, as the original exception context remains +available if needed (for example, if an intervening library has incorrectly +suppressed valuable underlying details):: + + >>> try: + ... D({}).x + ... except AttributeError as exc: + ... print(repr(exc.__context__)) + ... + KeyError('x',) + + PEP 3155: Qualified name for classes and functions ================================================== |