Is every value in the array an array?
This should only test the second array dimension of the array. The values of the nested arrays don't have to be arrays. 
Examples:
```python
[[1],[2]] => true
['1','2'] => false
[{1:1},{2:2}] => false
```
def arr_check(arr):
    for i in arr:
        try:
            i.append("")
        except:
            return False
    return True
def arr_check(arr):
    for i in arr:
        try:
            i.append("")
        except:
            return False
    return True