kopia lustrzana https://github.com/micropython/micropython-lib
contextlib: re-instate ExitStack from CPython 3.4
rodzic
1260289917
commit
e41f5da1ea
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@ -8,6 +8,8 @@ Not implemented:
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"""
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import sys
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from collections import deque
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from ucontextlib import *
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@ -64,3 +66,134 @@ class suppress:
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#
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# See http://bugs.python.org/issue12029 for more details
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return exctype is not None and issubclass(exctype, self._exceptions)
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# Inspired by discussions on http://bugs.python.org/issue13585
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class ExitStack(object):
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"""Context manager for dynamic management of a stack of exit callbacks
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For example:
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with ExitStack() as stack:
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files = [stack.enter_context(open(fname)) for fname in filenames]
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# All opened files will automatically be closed at the end of
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# the with statement, even if attempts to open files later
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# in the list raise an exception
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"""
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def __init__(self):
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self._exit_callbacks = deque()
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def pop_all(self):
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"""Preserve the context stack by transferring it to a new instance"""
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new_stack = type(self)()
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new_stack._exit_callbacks = self._exit_callbacks
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self._exit_callbacks = deque()
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return new_stack
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def _push_cm_exit(self, cm, cm_exit):
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"""Helper to correctly register callbacks to __exit__ methods"""
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def _exit_wrapper(*exc_details):
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return cm_exit(cm, *exc_details)
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_exit_wrapper.__self__ = cm
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self.push(_exit_wrapper)
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def push(self, exit):
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"""Registers a callback with the standard __exit__ method signature
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Can suppress exceptions the same way __exit__ methods can.
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Also accepts any object with an __exit__ method (registering a call
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to the method instead of the object itself)
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"""
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# We use an unbound method rather than a bound method to follow
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# the standard lookup behaviour for special methods
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_cb_type = type(exit)
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try:
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exit_method = _cb_type.__exit__
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except AttributeError:
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# Not a context manager, so assume its a callable
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self._exit_callbacks.append(exit)
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else:
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self._push_cm_exit(exit, exit_method)
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return exit # Allow use as a decorator
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def callback(self, callback, *args, **kwds):
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"""Registers an arbitrary callback and arguments.
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Cannot suppress exceptions.
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"""
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def _exit_wrapper(exc_type, exc, tb):
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callback(*args, **kwds)
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# We changed the signature, so using @wraps is not appropriate, but
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# setting __wrapped__ may still help with introspection
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_exit_wrapper.__wrapped__ = callback
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self.push(_exit_wrapper)
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return callback # Allow use as a decorator
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def enter_context(self, cm):
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"""Enters the supplied context manager
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If successful, also pushes its __exit__ method as a callback and
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returns the result of the __enter__ method.
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"""
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# We look up the special methods on the type to match the with statement
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_cm_type = type(cm)
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_exit = _cm_type.__exit__
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result = _cm_type.__enter__(cm)
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self._push_cm_exit(cm, _exit)
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return result
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def close(self):
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"""Immediately unwind the context stack"""
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self.__exit__(None, None, None)
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def __enter__(self):
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return self
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def __exit__(self, *exc_details):
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received_exc = exc_details[0] is not None
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# We manipulate the exception state so it behaves as though
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# we were actually nesting multiple with statements
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frame_exc = sys.exc_info()[1]
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def _fix_exception_context(new_exc, old_exc):
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# Context may not be correct, so find the end of the chain
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while 1:
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exc_context = new_exc.__context__
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if exc_context is old_exc:
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# Context is already set correctly (see issue 20317)
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return
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if exc_context is None or exc_context is frame_exc:
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break
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new_exc = exc_context
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# Change the end of the chain to point to the exception
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# we expect it to reference
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new_exc.__context__ = old_exc
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# Callbacks are invoked in LIFO order to match the behaviour of
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# nested context managers
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suppressed_exc = False
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pending_raise = False
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while self._exit_callbacks:
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cb = self._exit_callbacks.pop()
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try:
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if cb(*exc_details):
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suppressed_exc = True
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pending_raise = False
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exc_details = (None, None, None)
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except:
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new_exc_details = sys.exc_info()
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# simulate the stack of exceptions by setting the context
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_fix_exception_context(new_exc_details[1], exc_details[1])
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pending_raise = True
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exc_details = new_exc_details
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if pending_raise:
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try:
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# bare "raise exc_details[1]" replaces our carefully
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# set-up context
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fixed_ctx = exc_details[1].__context__
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raise exc_details[1]
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except BaseException:
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exc_details[1].__context__ = fixed_ctx
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raise
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return received_exc and suppressed_exc
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