def readId2Name(fin):
    """
    Reconstruct a global id=>username dictionary from an open csv file
    
    Reads the globalId2Name file (or equivalent) and constructs an id=>username
    dictionary. Input is an open csv.reader file such as the one constructed
    by the main method of this module. Returns a dictionary of id=>username
    """
    retDict = {}
    fin.readrow()
    for iden, name in fin:
        retDict[iden] = name
    return retDict