what does zip(*res) mean in python in the following code?
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In python, * is the 'splat' operator. It is used for unpacking a list into arguments. For example: foo(*[1, 2, 3]) is the same as foo(1, 2, 3) .
The zip() function takes n iterables, and returns y tuples, where y is the least of the length of all of the iterables provided. The y th tuple will contain the y th element of all of the iterables provided.
For example:
zip(['a', 'b', 'c'], [1, 2, 3])
Will yield
('a', 1) ('b', 2) ('c', 3)
For a nested list like res in the example you provided, calling zip(*res) will do something like this:
res = [['a', 'b', 'c'], [1, 2, 3]]
zip(*res)
# this is the same as calling zip(['a', 'b', 'c'], [1, 2, 3])
('a', 1)
('b', 2)
('c', 3)
zip(*res) transposes a matrix (2-d array/list). The * operator 'unpacks' an iterable or rows of a matrix and zip interleaves and zips the rows column-wise:
> x = [('a', 'b', 'c'), (1, 2, 3)]
> zip(*x)
[('a', 1), ('b', 2), ('c', 3)]
Imagine mirroring the matrix on the diagonal.
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