An oddity in list comparison and element assignment

[Tim Chase]

> As to containers,  would you say that envelope containing five $100
> bills is the same as an envelope containing a single $100 bill and 4
> xerox copies of it? If so, I'd like to engage in some envelope
> exchanges with you :-)

if len(set([bill.serialnumber for bill in envelope])) != 
len(envelope): refuseMichaelsExchange()

Though the way references work, you would have an envelope 
containing only  5 slips of paper that all say "I have a $100 
bill"...

:)

-tkc