class Field(object):

    def __init__(self, fid, sid, name, unit):
        self.fid = fid
        self.sid = sid
        self.name = name
        self.unit = unit

    def get_by_fid(self, fid):
        with sqlite3.connect("db.sqlite") as conn:
            results = conn.execute("SELECT * FROM fields WHERE fid=?;",[fid])
            result = results[0]
            return Field(result[0], result[1], result[2], result[3])

    def get_by_name(self, sid, name):
        with sqlite3.connect("db.sqlite") as conn:
            results = conn.execute("SELECT * FROM fields WHERE sid=? AND name=?;",[sid,name])
            result = results[0]
            return Field(result[0], result[1], result[2], result[3])

my_field = Field.get_by_fid(123)
print("Field name is: {}".format(my_field.name))