In Python or NumPy, what is the best way to find out the first occurrence of a subarray?

For example, I have 

```
a = [1, 2, 3, 4, 5, 6]
b = [2, 3, 4]

```

What is the fastest way (run-time-wise) to find out where b occurs in a? I understand for strings this is extremely easy, but what about for a list or numpy ndarray? 

Thanks a lot! 

[EDITED] I prefer the numpy solution, since from my experience numpy vectorization is much faster than Python list comprehension. Meanwhile, the big array is huge, so I don't want to convert it into a string; that will be (too) long.