What does pix[x, y] mean in Python

Question

I find a strange statement when I'm reading PIL document.

In 1.1.6 and later, load returns a pixel access object that can be used to read and modify pixels. The access object behaves like a 2-dimensional array, so you can do:

pix = im.load()
print pix[x, y]
pix[x, y] = value

What does pix[x, y] mean here? It's not slicing syntax because , used rather than :.

Answer 1

pix[x, y]

is the same as

t = x, y
pix[t]

or

t = (x, y)
pix[t]

or

pix[(x, y)]

What you're seeing is a tuple literal inside an item-getting expression, in the same way that I can nest other expressions such as l[1 if skip else 0]