I am struggling with an admittedly minor issue, but still...

When requesting historical data in research, I can do so with the Equity Ticker, such as "AAPL".
Nevertheless, in a multi-security request (see below), the DataFrame returned uses as level-0 index the Symbol, such as "AAPL R753QTJ8XC9X". I have searched around on how to get the full symbol string from the symbol object, but so far without success.

For clarification of the question, see the code:

# init the QuantBook --------------
qb = QuantBook()
# add some Equities --------------
spy = qb.AddEquity("SPY")
aapl = qb.AddEquity("AAPL")
goog = qb.AddEquity("GOOG")

# request history ------------
history = qb.History(qb.Securities.Keys,10)

# now, the level-0 key in history is NOT "SPY","AAPL" and "GOOG", but "SPY R735QTJ8XC9X","AAPL R735QTJ8XC9X" and "AAPL R735QTJ8XC9X" <- how can I get those ones from the Equity objects that I created previously with AddEquity, instead of doing some pattern matching (i.e. identify which keys start with "SPY")?