Statement (un)equality

Erik Max Francis max at alcyone.com
Fri Feb 20 11:50:19 CET 2004


Adam Przybyla wrote:

> >>> [[y,x] for x,y in [1,2],[3,4]]
> [[2, 1], [4, 3]]
> >>> map(lambda x,y: [y,x], [1,2],[3,4])
> [[3, 1], [4, 2]]
> >>>
> Why there is a difference? How to make the same thing like in map
> statement?

Because the same things aren't happening here, despite their outward
similarity.  For the second case to be equivalent to the first, you
really meant:

>>> map(lambda x: [x[1], x[0]], [[1, 2], [3, 4]])
[[2, 1], [4, 3]]

You can pass multiple sequences to map, and that interleaves the
results:

>>> map(lambda x, y, z: (x, y, z), [1, 2], [3, 4], [5, 6])
[(1, 3, 5), (2, 4, 6)]

-- 
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