Write a function in python how$\_$long that takes as input the amount for an initial investment, a final target amount, and the expected interest rate of the account $($as a decimal$),$ and it returns the number of years it will take to achieve the target amount.

For example, if you win a small lottery and decide to invest $50,000$ dollars today in the market, which historically averages a $7\%$ annual return, and you want to wait for it to become a million dollars, then how$\_$long$(50000,1000000,0\mathrm{.}07)$ should return $44\mathrm{.}27715216205352,$ telling you that it will take just over $44$ years.