Thanks for your reply.But the answer is not I except, I will show you some examples to explain what result I except: @contextmanagerdef cm(): print('open file') yield print('close file')with cm(): 1/0 If I use a contextmanager ,I except it can help me to close the file anytime,even raise an error,but if I define a function with @contextmanager like the example which I have showed for you, it will never print('close file') I can only modify it like this:@contextmanagerdef cm(): try: print('open file') yield except Exception as e: print('Error',e) finally: print('close file') It is not friendly for us to use it, so I modify the contextlib to fix it,you can catch it from the e-mail attachment.It's in the line 79 and line 97---------------------------------------------------------------------- 发件人:python-ideas-requ...@python.org 收件人:python-ideas@python.org 主题:Python-ideas Digest, Vol 146, Issue 13 日期:2019年01月06日 01点05分
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Re: Fixed point format for numbers with locale based separators (?ukasz Stelmach) ---------------------------------------------------------------------- Message: 1 Date: Sat, 5 Jan 2019 16:45:34 +0200 From: Serhiy Storchaka <storch...@gmail.com> To: python-ideas@python.org Subject: Re: [Python-ideas] Make the @contextmanager of contextlib to be a real contextmanager Message-ID: <q0qfqd$q1q$1...@blaine.gmane.org> Content-Type: text/plain; charset=UTF-8; format=flowed 05.01.19 14:52, Moon?sun ????: > As we know,when we import the module--'contextlib',we can use the > decorator '@contextmanager' and keyword ?yield? to make a 'instance' of > Class '_GeneratorContextManager' in 'contextlib' module,then we can use > it like: > with 'instance' as 'xx': > ? ? 'code block' > ? ? pass > But there is a little bug,when the code block raise a error,the instance > cannot run the code which after the keyword 'yield'. This is not a bug. Consider the following example: @contextmanager def cm(): try: yield except BaseException as err: print('Fail:', err) raise else: print('Success') with cm(): 1/0 What result would you expect? Test it with the stdlib implementation and with your implementation. ------------------------------ Message: 2 Date: Sat, 05 Jan 2019 16:41:20 +0100 From: ?ukasz Stelmach <steel...@post.pl> To: Steven D'Aprano <st...@pearwood.info> Cc: python-ideas@python.org Subject: Re: [Python-ideas] Fixed point format for numbers with locale based separators Message-ID: <87y37z9knz.fsf%steel...@post.pl> Content-Type: text/plain; charset="utf-8" Steven D'Aprano <st...@pearwood.info> writes: > On Fri, Jan 04, 2019 at 03:57:53PM +0100, ?ukasz Stelmach wrote: >> Hi, >> >> I would like to present two pull requests[1][2] implementing fixed point >> presentation of numbers and ask for comments. The first is mine. I >> learnt about the second after publishing mine. > > Before I look at the implementation, can you explain the functional > requirements please? As I stated in the original message below the table: >> In the application I want to create I am going to present users numbers >> ranging up to 3 orders of magnitude and I (my users) want them to be >> presented consistently with regards to number of decimal digits AND I >> want to conform to rules of languages of my users. And I would like to >> avoid the exponent notation by all means. The pint[1] library I use, implements formatting of physical quantities using the format()/__format__ code. As far as I can tell my patch for Python is shorter and more straightforward than a patch for pint to use locale.format(). Because the "g" based "n" formatter has been present since the advanced string formatting was described in PEP-3101, I think it is necessary to add the "m" formatter based on "f". The advanced string formatting facility in Python is very convenient and programmers shouldn't forced to use locale.format() like this "The total length of {} sticks is {} meters.".format(n_sticks, locale.format(".2f", l_sticks)) instead of "The total length of {} sticks is {:.2f} meters.".format(n_sticks, l_sticks) > In other words, what is the new feature you hope to have excepted? > Explain the intention and the API (the interface). The implementation is > the least important part :-) I wish to add a new formatter "m" for float/complex/decimal numbers, which behaves like the existing "f", but uses the decimal separator from the locale database. There is "n" formmatter which behaves like "g" but it does not fit my needs. > [...] >> Formatting 1.23456789 * n (LC_ALL=3Dpl_PL.UTF-8) >> | n | ".2f" | ".3n" | >> |---+----------+----------| >> | 1 | 1.23 | 1,23 | >> | 2 | 12.35 | 12,3 | >> | 3 | 123.46 | 123 | >> | 4 | 1234.57 | 1,23e+03 | > > I'm afraid I cannot work out what that table means. You say "Formatting > 1.23... * n" (multiplying by n) but the results shown aren't multiplied > by n=2, n=3, n=4 as the table suggests. > > Can you show what Python code you expect will produce the expected > output? for n in range(1,5): print("| {} | {:8.2f} | {:8.3n} |".format(n,1.23456789 * 10**n, 1.23456789 * 10**n)) [1] http://pint.readthedocs.io/ -- By?o mi bardzo mi?o. --- Rurku. --- ... >?ukasz< --- To dobrze, ?e mnie s?uchasz. -------------- next part -------------- A non-text attachment was scrubbed... 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"""Utilities for with-statement contexts. See PEP 343.""" import abc import sys import _collections_abc from collections import deque from functools import wraps __all__ = ["contextmanager", "closing", "AbstractContextManager", "ContextDecorator", "ExitStack", "redirect_stdout", "redirect_stderr", "suppress"] class AbstractContextManager(abc.ABC): """An abstract base class for context managers.""" def __enter__(self): """Return `self` upon entering the runtime context.""" return self @abc.abstractmethod def __exit__(self, exc_type, exc_value, traceback): """Raise any exception triggered within the runtime context.""" return None @classmethod def __subclasshook__(cls, C): if cls is AbstractContextManager: return _collections_abc._check_methods(C, "__enter__", "__exit__") return NotImplemented class ContextDecorator(object): "A base class or mixin that enables context managers to work as decorators." def _recreate_cm(self): """Return a recreated instance of self. Allows an otherwise one-shot context manager like _GeneratorContextManager to support use as a decorator via implicit recreation. This is a private interface just for _GeneratorContextManager. See issue #11647 for details. """ return self def __call__(self, func): @wraps(func) def inner(*args, **kwds): with self._recreate_cm(): return func(*args, **kwds) return inner class _GeneratorContextManager(ContextDecorator, AbstractContextManager): """Helper for @contextmanager decorator.""" def __init__(self, func, args, kwds): self.gen = func(*args, **kwds) self.func, self.args, self.kwds = func, args, kwds # Issue 19330: ensure context manager instances have good docstrings doc = getattr(func, "__doc__", None) if doc is None: doc = type(self).__doc__ self.__doc__ = doc # Unfortunately, this still doesn't provide good help output when # inspecting the created context manager instances, since pydoc # currently bypasses the instance docstring and shows the docstring # for the class instead. # See http://bugs.python.org/issue19404 for more details. def _recreate_cm(self): # _GCM instances are one-shot context managers, so the # CM must be recreated each time a decorated function is # called return self.__class__(self.func, self.args, self.kwds) def _next(self): # éè¿åå ä¸å±try,å¯ä»¥æè·next()卿§è¡å®ä»£ç åæåºçStopIterationå¼å¸¸ try: # éè¿æ·»å æ¤å¤ä»£ç ,å³å¯å®ç°è¿ç¨ä¸åºé®é¢æ æ³å ³éæä»¶çæ åµ next(self.gen) except StopIteration: return False else: raise RuntimeError("generator didn't stop") def __enter__(self): try: return next(self.gen) except StopIteration: raise RuntimeError("generator didn't yield") from None def __exit__(self, type, value, traceback): if type is None: self._next() else: # æ 论æ¯å¦ä¼ éäºé误ä¾ç¶æ§è¡next()æä½æ§è¡yieldåé¢çè¯å¥ try: self._next() finally: if value is None: # Need to force instantiation so we can reliably # tell if we get the same exception back value = type() try: self.gen.throw(type, value, traceback) except StopIteration as exc: # Suppress StopIteration *unless* it's the same exception that # was passed to throw(). This prevents a StopIteration # raised inside the "with" statement from being suppressed. return exc is not value except RuntimeError as exc: # Don't re-raise the passed in exception. (issue27122) if exc is value: return False # Likewise, avoid suppressing if a StopIteration exception # was passed to throw() and later wrapped into a RuntimeError # (see PEP 479). if type is StopIteration and exc.__cause__ is value: return False raise except: # only re-raise if it's *not* the exception that was # passed to throw(), because __exit__() must not raise # an exception unless __exit__() itself failed. But throw() # has to raise the exception to signal propagation, so this # fixes the impedance mismatch between the throw() protocol # and the __exit__() protocol. # if sys.exc_info()[1] is value: return False raise raise RuntimeError("generator didn't stop after throw()") def contextmanager(func): """@contextmanager decorator. Typical usage: @contextmanager def some_generator(<arguments>): <setup> try: yield <value> finally: <cleanup> This makes this: with some_generator(<arguments>) as <variable>: <body> equivalent to this: <setup> try: <variable> = <value> <body> finally: <cleanup> """ @wraps(func) def helper(*args, **kwds): return _GeneratorContextManager(func, args, kwds) return helper class closing(AbstractContextManager): """Context to automatically close something at the end of a block. Code like this: with closing(<module>.open(<arguments>)) as f: <block> is equivalent to this: f = <module>.open(<arguments>) try: <block> finally: f.close() """ def __init__(self, thing): self.thing = thing def __enter__(self): return self.thing def __exit__(self, *exc_info): self.thing.close() class _RedirectStream(AbstractContextManager): _stream = None def __init__(self, new_target): self._new_target = new_target # We use a list of old targets to make this CM re-entrant self._old_targets = [] def __enter__(self): self._old_targets.append(getattr(sys, self._stream)) setattr(sys, self._stream, self._new_target) return self._new_target def __exit__(self, exctype, excinst, exctb): setattr(sys, self._stream, self._old_targets.pop()) class redirect_stdout(_RedirectStream): """Context manager for temporarily redirecting stdout to another file. # How to send help() to stderr with redirect_stdout(sys.stderr): help(dir) # How to write help() to a file with open('help.txt', 'w') as f: with redirect_stdout(f): help(pow) """ _stream = "stdout" class redirect_stderr(_RedirectStream): """Context manager for temporarily redirecting stderr to another file.""" _stream = "stderr" class suppress(AbstractContextManager): """Context manager to suppress specified exceptions After the exception is suppressed, execution proceeds with the next statement following the with statement. with suppress(FileNotFoundError): os.remove(somefile) # Execution still resumes here if the file was already removed """ def __init__(self, *exceptions): self._exceptions = exceptions def __enter__(self): pass def __exit__(self, exctype, excinst, exctb): # Unlike isinstance and issubclass, CPython exception handling # currently only looks at the concrete type hierarchy (ignoring # the instance and subclass checking hooks). While Guido considers # that a bug rather than a feature, it's a fairly hard one to fix # due to various internal implementation details. suppress provides # the simpler issubclass based semantics, rather than trying to # exactly reproduce the limitations of the CPython interpreter. # # See http://bugs.python.org/issue12029 for more details return exctype is not None and issubclass(exctype, self._exceptions) # Inspired by discussions on http://bugs.python.org/issue13585 class ExitStack(AbstractContextManager): """Context manager for dynamic management of a stack of exit callbacks For example: with ExitStack() as stack: files = [stack.enter_context(open(fname)) for fname in filenames] # All opened files will automatically be closed at the end of # the with statement, even if attempts to open files later # in the list raise an exception """ def __init__(self): self._exit_callbacks = deque() def pop_all(self): """Preserve the context stack by transferring it to a new instance""" new_stack = type(self)() new_stack._exit_callbacks = self._exit_callbacks self._exit_callbacks = deque() return new_stack def _push_cm_exit(self, cm, cm_exit): """Helper to correctly register callbacks to __exit__ methods""" def _exit_wrapper(*exc_details): return cm_exit(cm, *exc_details) _exit_wrapper.__self__ = cm self.push(_exit_wrapper) def push(self, exit): """Registers a callback with the standard __exit__ method signature Can suppress exceptions the same way __exit__ methods can. Also accepts any object with an __exit__ method (registering a call to the method instead of the object itself) """ # We use an unbound method rather than a bound method to follow # the standard lookup behaviour for special methods _cb_type = type(exit) try: exit_method = _cb_type.__exit__ except AttributeError: # Not a context manager, so assume its a callable self._exit_callbacks.append(exit) else: self._push_cm_exit(exit, exit_method) return exit # Allow use as a decorator def callback(self, callback, *args, **kwds): """Registers an arbitrary callback and arguments. Cannot suppress exceptions. """ def _exit_wrapper(exc_type, exc, tb): callback(*args, **kwds) # We changed the signature, so using @wraps is not appropriate, but # setting __wrapped__ may still help with introspection _exit_wrapper.__wrapped__ = callback self.push(_exit_wrapper) return callback # Allow use as a decorator def enter_context(self, cm): """Enters the supplied context manager If successful, also pushes its __exit__ method as a callback and returns the result of the __enter__ method. """ # We look up the special methods on the type to match the with statement _cm_type = type(cm) _exit = _cm_type.__exit__ result = _cm_type.__enter__(cm) self._push_cm_exit(cm, _exit) return result def close(self): """Immediately unwind the context stack""" self.__exit__(None, None, None) def __exit__(self, *exc_details): received_exc = exc_details[0] is not None # We manipulate the exception state so it behaves as though # we were actually nesting multiple with statements frame_exc = sys.exc_info()[1] def _fix_exception_context(new_exc, old_exc): # Context may not be correct, so find the end of the chain while 1: exc_context = new_exc.__context__ if exc_context is old_exc: # Context is already set correctly (see issue 20317) return if exc_context is None or exc_context is frame_exc: break new_exc = exc_context # Change the end of the chain to point to the exception # we expect it to reference new_exc.__context__ = old_exc # Callbacks are invoked in LIFO order to match the behaviour of # nested context managers suppressed_exc = False pending_raise = False while self._exit_callbacks: cb = self._exit_callbacks.pop() try: if cb(*exc_details): suppressed_exc = True pending_raise = False exc_details = (None, None, None) except: new_exc_details = sys.exc_info() # simulate the stack of exceptions by setting the context _fix_exception_context(new_exc_details[1], exc_details[1]) pending_raise = True exc_details = new_exc_details if pending_raise: try: # bare "raise exc_details[1]" replaces our carefully # set-up context fixed_ctx = exc_details[1].__context__ raise exc_details[1] except BaseException: exc_details[1].__context__ = fixed_ctx raise return received_exc and suppressed_exc
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