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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 ModifyNodeStorageUnits(r, node, storage_type, name, allocatable=None):
 """ Modifies parameters of storage units on the node. @type node: str @param node: node whose storage units to modify @type storage_type: str @param storage_type: storage type whose units to modify @type name: str @param name: name of the storage unit @type allocatable: bool or None @param allocatable: Whether to set the "allocatable" flag on the storage unit (None=no modification, True=set, False=unset) @rtype: int @return: job id """


    query = {
        "storage_type": storage_type,
        "name": name,
    }

    if allocatable is not None:
        query["allocatable"] = allocatable

    return r.request("put", "/2/nodes/%s/storage/modify" % node, query=query)