Ben Bush said unto the world upon 2005-11-15 01:24:
<top posting corrected and post trimmed>
>
> Unfortunately, the indents got screwed up along the way. But the part
>
>>of my code you asked about was:
>>
>>for item in list1:
>> if item in list2:
>> if item + 1 in list1 and item + 1 in list2:
>> return True
>>
>>In some detail:
<snip my detailed explanation>
>>Does that clarify it?
>>
>>Finally, your response to Alex would have been much more useful if
>>you'd quoted the error rather than just asserting that you got an
>>error :-)
>>
>>Best,
>>
>>Brian vdB
Hi Ben,
first, while there are those on the list/n.g. who differ, the
majoritarian view is that top posting isn't a good thing. At minimum,
if someone bothered to correct it, it would be nice if in a further
follow-up you didn't top-post again :-)
Second, you might find the tutor list really helpful. It is where I
learned most of what I know, and I still read it more than c.l.p. It
is very newbie friendly.
As for your question:
>> Hi Brian,
>
> regarding "if item + 1 in list1 and item + 1 in list2:",
> my understanding is this will check whether the following item in
each list
> is the same. How does the code permit the situation that the order
does not
> matter?
> For example, for lisA and lisB, the comparison is true and the two
lists
> have 5 and 6 but different order.
> lisA=[1,2,3,4,5,6,9]
> lisB=[1,6,5]
> Many Thanks!
There are two distinct issues that might be the source of your
confusion. I will be explicit about both; pardon if only one applied.
>>> num_list = [1, 42, 451]
>>> for item in num_list: print item, type(item)
1 <type 'int'>
42 <type 'int'>
451 <type 'int'>
>>>
Iterating over a list as I did makes item refer to each list member in
turn. So, item + 1 doesn't refer to the next item (except by accident
as it were when two items are sequential ints). Rather, it refers to
int that results from adding 1 to the int that is item.
You might be thinking of list index notation instead:
>>> index = 1
>>> num_list[index], num_list[index + 1]
(42, 451)
>>>
(General tip: putting a print or two in my original code would have
cleared that up very quickly.)
So, that cleared up, are you wondering why item + 1 suffices, instead
of both item + 1 and item - 1?
If so, consider that it the list1 has both n and n - 1 in it and we
iterate over list1 checking each case, eventually item will refer to n
- 1. In that case, item + 1 = n and we are covered after all. I did as
I did in my original code thinking it was probably quicker to have
only one test and pay the cost that there might be a quicker exit from
the iteration were I to test both item + 1 and item - 1. f it
mattered, I'd test for speed. Of course, if speed mattered and I could
ever remember to use sets :-) I'd follow Alex and Duncan's suggestions
instead!
If that doesn't clear it up, give yourself a few short lists and run
test cases having inserted print statements to see what is going on.
To stop it all from whizzing by too fast, put in
raw_input("Hit enter and I'll keep working")
somewhere in the loops to slow things down.
HTH,
Brian vdB
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