Consider the following function definition:
flatten_by_nesting_depth(nested_lst )
The function is given a nested list of integers nested_list. When called, it should create and return a flat list of integers containing all the numbers in nested_list. The numbers should show in the returned list by their nesting depth. That is, first will come all the numbers with nesting depth 1, then would come all the numbers with nesting depth 2, followed by the numbers with nesting depth 3, etc. Note: The order of the numbers with the same nested depth does not matter.
For example, if nested_list is the nested list demonstrated above, the call flatten_by_nesting_depth(nested_lst ) could return:
[3, 9, 1, 2, 4, 8, 5, 6, 7].