Memory leak with modular symbols?

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I run the following code:

DB = CremonaDatabase()
for N in range(1,10000):
        Cs = DB.isogeny_classes(N)
        for C in Cs:
                E=EllipticCurve(C[0][0])
                phi=E.modular_symbol()

and the memory used keeps going up and up and up.

This must be related to the fact that the modular symbol data is cached. Is there a way I can clear out this memory usage? I want to be doing a computation with each such modular symbol and then just get rid of the modular symbol.