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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 malloc(self, key, shape, dtype):
 """Allocates a block of shared memory, and returns a numpy array whose data corresponds with that block. Args: key (str):
 The key to identify the block. shape (list of int):
 The shape of the numpy array to allocate. dtype (type):
 The numpy data type (e.g. np.float32). Returns: np.ndarray: The numpy array that is positioned on the shared memory. """

        if key not in self._memory or self._memory[key].shape != shape or self._memory[key].dtype != dtype:
            self._memory[key] = Shmem(key, shape, dtype, self._uuid)

        return self._memory[key].np_array