On Wed, Apr 30, 2014 at 10:21:41PM -0700, Scott W Dunning wrote:
> So, I get a little confused about lists sometimes. This one is a
> little hard to make heads or tails of. I get confused about how to
> tell how many lists are within one list like the one below. How many
> lists are located inside alist is it 1 or 2, 3?? Also, do spaces
> count as an index in lists?
>
> >>> alist = [3, 67, "cat”, [56, 57, “dog”], [], 3.14, False]
> >>> print alist[4:]
> [[], 3.14, False]
Spaces do not count as indexes. Spaces are just inserted when printing
the list to make it easier for people to read. It is commas, not spaces,
which separate items in the list. So you have:
alist = [3, 67, "cat", [56, 57, "dog"], [], 3.14, False]
Count the items separated by commas:
3 comma <== that's one
67 comma <== that's two
"cat" comma <== three
Next is tricky: the square bracket [ starts a new list. Since we don't
care how many items are inside that list, we just keep going until we
reach a matching ] closing square bracket:
[56, 57, "dog"] comma <== that's four
[] comma <== five
3.14 comma <== six
False <== seventh and last
Notice that because the commas *separate* items, there is one more item
than separators: 1,2,3,4,5,6,7 (six commas and seven items).
Also notice that out of the seven items inside alist, only two of
them are lists:
3 INTEGER
67 INTEGER
"cat" STRING
[56, 57, "dog"] LIST with three items
[] LIST with zero items
3.14 FLOAT
False BOOLEAN FLAG
> The ouput for below is 2 when it seems like there should be 3 lists
> located inside x. Is it [10,20] that is not consider inside of x?
> Any tips on how to tell how to spot them more clearly?
>
> x = ['a', [2.0, 5, [10, 20]]]
> print len(x)
Again, look at the commas:
'a' (a string) comma <== first item
The next item begins with a square bracket, so it is a list. We ignore
everything inside it *except more square brackets* until we reach the
matching square bracket:
[2.0 comma (but we don't care)
5 comma (still don't care)
[ (and now we start yet another list, inside a list inside a list!)
10 comma (don't care)
20 (don't care)
] (we have reached the end of the innermost list)
] (we have reached the end of the inner list
and no more items after that. So the list called "x" has two items:
- the string "a"
- a list containing 2.0, 5, and another list
So there are two items inside list "x", three items inside the list
inside "x", and two items inside the list inside that.
When in doubt, this may help make it more obvious:
x = ['a', [2.0, 5, [10, 20]]]
for item in x:
print(item)
That will show you each item in turn.
--
Steven
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