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"""Utilities for with-statement contexts.  See PEP 343."""
from functools import wraps
__all__ = ["contextmanager", "nested", "closing"]
class GeneratorContextManager(object):
    """Helper for @contextmanager decorator."""
    def __init__(self, gen):
        self.gen = gen
    def __enter__(self):
        try:
            return self.gen.next()
        except StopIteration:
            raise RuntimeError("generator didn't yield")
    def __exit__(self, type, value, traceback):
        if type is None:
            try:
                self.gen.next()
            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, 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:
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
@contextmanager
def nested(*managers):
    """Support multiple context managers in a single with-statement.
    Code like this:
        with nested(A, B, C) as (X, Y, Z):
            <body>
    is equivalent to this:
        with A as X:
            with B as Y:
                with C as Z:
                    <body>
    exits = []
    vars = []
    exc = (None, None, None)
        for mgr in managers:
            exit = mgr.__exit__
            enter = mgr.__enter__
            vars.append(enter())
            exits.append(exit)
        yield vars
    except:
        exc = sys.exc_info()
    finally:
        while exits:
            exit = exits.pop()
            try:
                if exit(*exc):
                    exc = (None, None, None)
            except:
                exc = sys.exc_info()
        if exc != (None, None, None):
            # Don't rely on sys.exc_info() still containing
            # the right information. Another exception may
            # have been raised and caught by an exit method
            raise exc[0], exc[1], exc[2]
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()
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