Why does sys.getrefcount() return 2?

When you call getrefcount(), the reference is copied by value into the function's argument, temporarily bumping up the object's reference count. This is where the second reference comes from.

This is explained in the documentation:

The count returned is generally one higher than you might expect, because it includes the (temporary) reference as an argument to getrefcount().

As to your second question:

If I "del a", will the "numpy.array([1.2,3.4])" object still be there (no garbage collection)?

By the time getrefcount() exits, the array's reference count will to back to 1, and a subsequent del a would release the memory.