Beginners question.

[Player]

Hi all

I am teaching myself python and so am following a few tutorials from
online.

In one of the tutorials an exercise is the following...

As an exercise, write a loop that traverses the previous list and prints
the length of each element.

Firstly I just wanted to see if I could get the length out of those elements
that were list type.
I no thats not exactly what the exercise asks for, but I thought I would
start there.
However I am stuck and cant figure out why my code is doing what it's doing.
My code is as follows....

mylist = [1, 2, ["three", "four"], "five"]
for item in mylist:
if item == type(list):
myitem = len(item)
print myitem
else:
print item

All my code seems to do is print out each element of the list on a new line.
What I had expected it to do was this....
1
2
2
'five'

but it doesn't, what it does do is this...

1
2
['three', 'four']
'five'

I expected the line,
myitem = len(item)
to issue the variable, myitem, with a value that was the length of item.
But as you cans ee it doesn't and simply ignores all that code and does the
else:
print item
part instead, misisng out the first half of the for loop.

Were am I going wrong ??

Thanks in advance for any help

M.B aka - Player -

--
*************
The Imagination may be compared to Adam's dream-
he awoke and found it truth.
John Keats.
*************

 

[Russell Blau]

Firstly I just wanted to see if I could get the length out of those

elements > that were list type.

I no thats not exactly what the exercise asks for, but I thought I would
start there.
However I am stuck and cant figure out why my code is doing what it's doing.
My code is as follows....

mylist = [1, 2, ["three", "four"], "five"]
for item in mylist:
if item == type(list):

The "if" statement above is always false (well, at least for any list you
are likely to encounter in real life), because you are looking to see if the
item is equal to "type(list)" which is a type object. I think you meant:

if type(item) == list:

That's why your len() statement was never being reached.

 

[Jeremy Bowers]

mylist = [1, 2, ["three", "four"], "five"]
for item in mylist:
if item == type(list):
myitem = len(item)
print myitem
else:
print item

General tip: Don't forget how much fun the interpreter is:

Python 2.3.4 (#1, Jun 8 2004, 17:41:43)
[GCC 3.3.3 20040217 (Gentoo Linux 3.3.3, propolice-3.3-7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.

item = ["three", "four"] # since this is the one we wonder about
item == type(list) False
# Uh-oh, there's the problem, let's see if we can get a clue: ....
item ['three', 'four']
type(list)

# Clearly, there's something wrong here; try Russell's solution: ....
type(item)

list

# Ah ha! ....

 

[Player]

[edit:snip]

Ok thanks Russell Blau I can see it now heh.

M.B -aka- Player

 

[Alex Martelli]

if item == type(list):

It's very unlikely that the item will equal the type of list (which is
the builtin metaclass 'type' itself). You presumably mean:

if isinstance(item, list):


Alex