Comma index in python list bracket

While numpy behaves the same way with the two, they are technically different.

You can see the difference by implementing __getitem__ yourself:

class GetitemTest(object):
    def __getitem__(self, item):
        print("getting: %r" %(item, ))
        return self

Then:

>>> x = GetitemTest()
>>> x[1,2]
getting: (1, 2)
<__main__.GetitemTest object at 0x10bb6d810>

>>> x[1][2]
getting: 1
getting: 2
<__main__.GetitemTest object at 0x10bb6d810>

Notice that x[1,2] only calls __getitem__ once, but x[1][2] calls it twice.

This is Numpy special ability.
Numpy official docs
"Unlike lists and tuples, numpy arrays support multidimensional indexing for multidimensional arrays. That means that it is not necessary to separate each dimension’s index into its own set of square brackets."

>>> x.shape = (2,5) # now x is 2-dimensional
>>> x[1,3]
8
>>> x[1,-1]
9