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Diffstat (limited to 'tests/bytecode/pylib-tests/contextlib.py')
| -rw-r--r-- | tests/bytecode/pylib-tests/contextlib.py | 255 |
1 files changed, 255 insertions, 0 deletions
diff --git a/tests/bytecode/pylib-tests/contextlib.py b/tests/bytecode/pylib-tests/contextlib.py new file mode 100644 index 0000000000..0b6bf71b08 --- /dev/null +++ b/tests/bytecode/pylib-tests/contextlib.py @@ -0,0 +1,255 @@ +"""Utilities for with-statement contexts. See PEP 343.""" + +import sys +from collections import deque +from functools import wraps + +__all__ = ["contextmanager", "closing", "ContextDecorator", "ExitStack"] + + +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): + """Helper for @contextmanager decorator.""" + + def __init__(self, func, *args, **kwds): + self.gen = func(*args, **kwds) + self.func, self.args, self.kwds = func, args, kwds + + 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 __enter__(self): + try: + return next(self.gen) + except StopIteration: + raise RuntimeError("generator didn't yield") + + def __exit__(self, type, value, traceback): + if type is None: + try: + next(self.gen) + except StopIteration: + return + else: + raise RuntimeError("generator didn't stop") + else: + 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) + raise RuntimeError("generator didn't stop after throw()") + except StopIteration as exc: + # Suppress the exception *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: + # 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 not value: + raise + + +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(object): + """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() + + +# Inspired by discussions on http://bugs.python.org/issue13585 +class ExitStack(object): + """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 __enter__(self): + return self + + def __exit__(self, *exc_details): + # 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): + while 1: + exc_context = new_exc.__context__ + if exc_context in (None, frame_exc): + break + new_exc = exc_context + new_exc.__context__ = old_exc + + # Callbacks are invoked in LIFO order to match the behaviour of + # nested context managers + suppressed_exc = False + while self._exit_callbacks: + cb = self._exit_callbacks.pop() + try: + if cb(*exc_details): + suppressed_exc = True + 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]) + if not self._exit_callbacks: + raise + exc_details = new_exc_details + return suppressed_exc |