AJW AJW - 13 days ago 7
Python Question

zip lists in python

I am a python newbie and I am trying to learn how to "zip" lists. To this end, I have a program, where at a particular point, I do the following:

x1, x2, x3 = stuff.calculations(withdataa)


This gives me three lists,
x1
,
x2
, and
x3
, each of, say, size 20.

Now, I do:

zipall = zip(x1, x2, x3)


However, when I do:

print "len of zipall %s" % len(zipall)


I get 20, which is not what I expected. I expected three. I think I am doing something fundamentally wrong.

NPE NPE
Answer

When you zip() together three lists containing 20 elements each, the result has twenty elements. Each element is a three-tuple.

See for yourself:

In [1]: a = b = c = range(20)

In [2]: zip(a, b, c)
Out[2]: 
[(0, 0, 0),
 (1, 1, 1),
 ...
 (17, 17, 17),
 (18, 18, 18),
 (19, 19, 19)]

To find out how many elements each tuple contains, you could examine the length of the first element:

In [3]: result = zip(a, b, c)

In [4]: len(result[0])
Out[4]: 3

Of course, this won't work if the lists were empty to start with.

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