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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def close(self) -> None: """Destroys this HTTP client, freeing any file descriptors used. This method is **not needed in normal use** due to the way that `AsyncHTTPClient` objects are transparently reused. ``close()`` is generally only necessary when either the `.IOLoop` is also being closed, or the ``force_instance=True`` argument was used when creating the `AsyncHTTPClient`. No other methods may be called on the `AsyncHTTPClient` after ``close()``. """

        if self._closed:
            return
        self._closed = True
        if self._instance_cache is not None:
            cached_val = self._instance_cache.pop(self.io_loop, None)
            # If there's an object other than self in the instance
            # cache for our IOLoop, something has gotten mixed up. A
            # value of None appears to be possible when this is called
            # from a destructor (HTTPClient.__del__) as the weakref
            # gets cleared before the destructor runs.
            if cached_val is not None and cached_val is not self:
                raise RuntimeError("inconsistent AsyncHTTPClient cache")