$6\mathrm{.}4$

Write a function called my$\_$pi$()$ that will return an approximation of PI $(3\mathrm{.}14159..).$ Use the Leibniz approximation $,$ which shows that you can approximate $\frac{1}{4}$ of PI with the following series:

$\frac{}{4}=1-\frac{1}{3}+\frac{1}{5}-\frac{1}{7}+\frac{1}{9}-$cdots$={\displaystyle \underset{k=0}{\overset{}{}}}\frac{(-1{)}^k}{2k+1}$