an_array = np.where(an_array > 20, 0, an_array)
Here is what the above code is Doing:
1. We create a new array, `an_array`, and set it equal to the numbers 1 through 30 (inclusive).
2. We use `np.where()` to find the indices of all elements in `an_array` that are greater than 20.
3. We then set all of the values found in step 2 to 0.
4. We print `an_array` to the console.