convert from from_currency to to_currency using cached info

def convert(from_currency, to_currency, from_currency_price=1):
	""" convert from from_currency to to_currency using cached info """
	get_cache()
	from_currency, to_currency = validate_currency(from_currency, to_currency)
	update_cache(from_currency, to_currency)
	return ccache[from_currency][to_currency]['value'] * from_currency_price