Convert list into rows based on previous condition

Question

I Have a datase like this

Column A	Column B
Cell 1	[ 1, 2 ,3 , 4]
Cell 2	[a,b,c]

but i want to convert it to like below using pyhton

Column A	Column B
Cell 1	1
Cell 1	2
Cell 1	3
Cell 1	4
Cell 2	a
Cell 2	b
Cell 2	c