Solve the programming task below in a Python markdown code block.
Mash 2 arrays together so that the returning array has alternating elements of the 2 arrays . Both arrays will always be the same length.

eg. [1,2,3] + ['a','b','c'] =  [1, 'a', 2, 'b', 3, 'c']
Also feel free to reuse/extend the following starter code:
```python
def array_mash(a, b):
```