list - Python Array Slice With Comma?

Question

I was wondering what the use of the comma was when slicing Python arrays - I have an example that appears to work, but the line that looks weird to me is

p = 20*numpy.log10(numpy.abs(numpy.fft.rfft(data[:2048, 0])))

Now, I know that when slicing an array, the first number is start, the next is end, and the last is step, but what does the comma after the end number designate? Thanks.

Answer 1

It is being used to extract a specific column from a 2D array. Refer to the first examples here.

So your example would extract column 0 (the first column) from the first 2048 rows (0 to 2047). Note however that this syntax will only work for numpy arrays and not general python lists.