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...getattr and iter built-in functions. When called with two arguments, next catches the StopIteration exception and returns the sentinel value instead of propagating the exception. This creates a nice duality between iter and next: iter(function, sentinel) <--> next(iterator, sentinel) Previous Proposals This proposal is not a new idea. The idea proposed here was supported by the BDFL on python-dev [1] and is even mentioned in the original iterator PEP, PEP 234: (In retrospect, it mig...
...getattr(metaclass, '__prepare__', None) if prepare is not None: return prepare(name, bases, **kwargs) else: return dict() The example above illustrates how the arguments to 'class' are interpreted. The class name is the first argument, followed by an arbitrary length list of base classes. After the base classes, there may be one or more keyword arguments, one of which can be metaclass. Note that the metaclass argument is not included in kwargs, since it is filtered out b...
...GetAttr() and PyObject_SetAttr() now accept Unicode objects for the attribute name. See note on getattr() above. A few bug fixes to argument processing for Unicode. PyArg_ParseTupleAndKeywords() now accepts "es#" and "es". PyArg_Parse() special cases "s#" for Unicode objects; it returns a pointer to the default encoded string data instead of to the raw UTF-16. Py_BuildValue accepts B format (for bgen-generated code). Internals On Unix, fix code for finding ...
...getattro and tp_setattro implementation, almost all built-in objects now place PyObject_GenericGetAttr and (if they have any writable attributes) PyObject_GenericSetAttr in their tp_getattro and tp_setattro slots. (Or, they can leave these NULL, and inherit them from the default base object, if they arrange for an explicit call to PyType_InitDict() for the type before the first instance is created.) In the simplest case, PyObject_GenericGetAttr() does exactly one dictionary lookup: it looks up...
...getattr(the_stmt, "__enter__", None) stmt_exit = getattr(the_stmt, "__exit__", None) if stmt_enter is None or stmt_exit is None: raise TypeError("Statement template required") VAR1 = stmt_enter() # Omit 'VAR1 =' if no 'as' clause exc = (None, None, None) try: try: BLOCK1 except: exc = sys.exc_info() raise finally: stmt_exit(*exc) Other than VAR1, none of the local variables shown above will be visible to user code. Like the iteration variable in a for l...
...getattr__ implementation would be hidden, and similarly for ?[] and __getitem__ implementations. Similarly, simple typing errors such as {}?.ietms() could go unnoticed. Existing conventions for handling these kinds of errors in the form of the getattr builtin and the .get(key, default) method pattern established by dict show that it is already possible to explicitly use this behaviour. As this approach would hide errors in code, it is rejected. None-aware Function Call The None-aware syntax ap...
...getattr, setattr and delattr operations now map to getitem, setitem and delitem on the celldict. The type of <module>.__dict__ and globals() is probably the only backwards incompatibility. When a module is initialized, its __builtins__ is initialized from the __builtin__ module's __dict__, which is itself a celldict. For each cell in __builtins__, the new module's __dict__ adds a cell with a NULL objptr, whose cellptr points to the corresponding cell of __builtins__. Python pseudo-code (...
...getattr__(self, attr): ... if attr[0] != '_': ... return getattr(obj, attr) ... else: ... raise AttributeError, attr ... return Wrapper() >>> class Test: ... public = 2 ... _private = 3 >>> w = make_wrapper(Test()) >>> w.public 2 >>> w._private Traceback (most recent call last): File "<stdin>", line 1, in ? AttributeError: _private An example from Tim Peters demonstrates the potential...
...getattribute__(self, attr): if attr == '__call__': return lambda: '__getattribute__' a = A() assert a() == '__call__' assert a.__call__() == '__getattribute__' In any case, with the renaming of __builtin__.super to __builtin__.__super__ this issue goes away entirely. Reference Implementation It is impossible to implement the above specification entirely in Python. This reference implementation has the following differences to the specification: New super semantics are i...
...getattr(v, '__set_name__', None) if func is not None: func(self, k) super(self, self).__init_subclass__(**kwargs) return self def __init__(self, name, bases, ns, **kwargs): super().__init__(name, bases, ns) class NewObject(object): @classmethod def __init_subclass__(cls): pass Reference Implementation The reference implementation for this PEP is attached to issue 27366. Backward compatibility issues The exact calling ...
...getattr(itr, "__exit__", None) if ext is not None: VAR1 = ext(*exc) # May re-raise *exc else: raise exc[0], exc[1], exc[2] else: VAR1 = itr.next() # May raise StopIteration except StopIteration: if ret: return val break try: ret = False val = exc = None BLOCK1 except: exc = sys.exc_info() (However, the variables 'itr' etc. are not user-visible an...
...getattr(self._cls, attr) def __setitem__(self, attr, value): setattr(self._cls, attr, value) def __delitem__(self, attr): delattr(self._cls, attr) def extend(cls): return lambda: ClassNamespace(cls) class Example: pass class ExtendedExample(namespace=extend(Example)): a = 1 b = 2 c = 3 >>> Example.a, Example.b, Example.c (1, 2, 3) Rejected Design Options Calling __autodecorate__ from type.__init__ Calling the new hook automatically fr...
...getattr(cls, "__match_args__", ())) is called. If this raises an exception the exception bubbles up. If the returned value is not a tuple, the conversion fails and TypeError is raised. If there are more positional patterns than the length of __match_args__ (as obtained using len()), TypeError is raised. Otherwise, positional pattern i is converted to a keyword pattern using __match_args__[i] as the keyword, provided it the latter is a string; if it is not, TypeError is raised. For duplicate keyw...
...getattr__() has been added to the collections module to emit a DeprecationWarning upon first access to an attribute: def __getattr__(name): # For backwards compatibility, continue to make the collections ABCs # through Python 3.6 available through the collections module. # Note: no new collections ABCs were added in Python 3.7 if name in _collections_abc.__all__: obj = getattr(_collections_abc, name) import warnings warnings.warn("Using or importing the A...
...getattr with three arguments) warp the code into looking like literal strings rather than attribute lookup, which can impact readability. A convenient EAFP notation solves all of this. There's no convenient way to write a helper function to do this; the nearest is something ugly using either lambda: def except_(expression, exception_list, default): try: return expression() except exception_list: return default() value = except_(lambda: 1/x, ZeroDivisionError, lambda: flo...
...getattr(type(_iter), "__iterclose__", lambda: None) try: traditional-for VAR in _iter: LOOP-BODY else: ELSE-BODY finally: _iterclose(_iter) where the "traditional-for statement" here is meant as a shorthand for the classic 3.5-and-earlier for loop semantics. Besides the top-level for statement, Python also contains several other places where iterators are consumed. For consistency, these should call __iterclose__ as well using semantics equivalent to the above. This ...
...getattr() operation with AttributeError exceptions changed into ImportError. "from M import *" now looks for M.__all__ to decide which names to import; if M.__all__ doesn't exist, it uses M.__dict__.keys() but filters out names starting with '_' as before. Whether or not __all__ exists, there's no restriction on the type of M. File objects have a new method, xreadlines(). This is the fastest way to iterate over all lines in a file: for line in file.xreadlines(): ...do something to...
...getattr(Spam, 'async')) # The coroutine can be executed and will print '42' Backwards Compatibility This proposal preserves 100% backwards compatibility. asyncio asyncio module was adapted and tested to work with coroutines and new statements. Backwards compatibility is 100% preserved, i.e. all existing code will work as-is. The required changes are mainly: Modify @asyncio.coroutine decorator to use new types.coroutine() function. Add __await__ = __iter__ line to asyncio.Future class. Add ...
...getattr(local, 'x', None) local.x = 'something' def __suspend__(self): local.x = self.old_x def __resume__(self): local.x = 'something' def __exit__(self, *err): local.x = self.old_x The downside of this approach is the addition of significant new complexity to the context manager protocol and the interpreter implementation. This approach is also likely to negatively impact the performance of generators and coroutines. Additionally, the solution i...
...getattr(cls, "__match_args__", _SENTINEL)). If this raises an exception the exception bubbles up. If the returned value is not a list, tuple, or None, the conversion fails and TypeError is raised at runtime. This means that only types that actually define __match_args__ will be usable in class defined patterns. Types that don't define __match_args__ will still be usable in instance attribute patterns. If __match_args__ is None, then only a single positional subpattern is permitted. Attempting to...