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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 sdram_alloc_for_vertices(controller, placements, allocations, core_as_tag=True, sdram_resource=SDRAM, cores_resource=Cores, clear=False):
 """Allocate and return a file-like view of a region of SDRAM for each vertex which uses SDRAM as a resource. The tag assigned to each region of assigned SDRAM is the index of the first core that each vertex is assigned. For example:: placements = {vertex: (0, 5)} allocations = {vertex: {Cores: slice(3, 6), SDRAM: slice(204, 304)}} sdram_allocations = sdram_alloc_for_vertices( controller, placements, allocations ) Will allocate a 100-byte block of SDRAM for the vertex which is allocated cores 3-5 on chip (0, 5). The region of SDRAM will be tagged `3` (because this is the index of the first core). Parameters controller : :py:class:`rig.machine_control.MachineController` Controller to use to allocate the SDRAM. Mapping of vertices to the chips they have been placed on. Same as produced by placers. Mapping of vertices to the resources they have been allocated. A block of memory of the size specified by the `sdram_resource` (default: :py:class:`~rig.place_and_route.SDRAM`) resource will be allocated for each vertex. Note that location of the supplied allocation is *not* used. When `core_as_tag=True`, the tag allocated will be the ID of the first core used by the vertex (indicated by the `cores_resource`, default :py:class:`~rig.place_and_route.Cores`), otherwise the tag will be set to 0. clear : bool If True the requested memory will be filled with zeros before the pointer is returned. If False (the default) the memory will be left as-is. Other Parameters core_as_tag : bool Use the index of the first allocated core as the tag for the region of memory, otherwise 0 will be used. sdram_resource : resource (default :py:class:`~rig.place_and_route.SDRAM`) Key used to indicate SDRAM usage in the resources dictionary. cores_resource : resource (default :py:class:`~rig.place_and_route.Cores`) Key used to indicate cores which have been allocated in the allocations dictionary. Returns ------- A file-like object for each vertex which can be used to read and write to the region of SDRAM allocated to the vertex. Raises ------ rig.machine_control.machine_controller.SpiNNakerMemoryError If the memory cannot be allocated, or a tag is already taken or invalid. """

    # For each vertex we perform an SDRAM alloc to get a file-like for
    # the vertex.
    vertex_memory = dict()
    for vertex, allocs in six.iteritems(allocations):
        if sdram_resource in allocs:
            sdram_slice = allocs[sdram_resource]
            assert sdram_slice.step is None

            size = sdram_slice.stop - sdram_slice.start
            x, y = placements[vertex]

            if core_as_tag:
                tag = allocs[cores_resource].start
            else:
                tag = 0

            # Get the memory
            vertex_memory[vertex] = controller.sdram_alloc_as_filelike(
                size, tag, x=x, y=y, clear=clear
            )

    return vertex_memory