initializing members of a list

Question

I want to initialize a list in python. I do not understand why the code below does not work:

u = ['abc', 'de', 'fghi', 'jklm', 'n', '']
for item in u:
 item = len(item)

There are other ways to initialize the list, like:

u = [len(item) for item in u]

But, my question is why the first code does not work.

Edit: I am a newbie to Python, and programming. Unfortunately I do not understand some parts of your answers. For example:
- rebinding in "rebinding the name item to the length of the name item "
- iterator in "item" is a temporary variable that points to an element of a u based on where the (implicit) iterator is pointing
As far as I understand, my second example, creates a new_list in memory, and assigns the values of new_list to u. No matter what the previous values were. But I want to know how I can change the values, in the first list. Thanks

Answer 1

In the first case, you are not initializing anything. "item" is a temporary variable that points to an element of a u based on where the (implicit) iterator is pointing. If you want to initialize a list in the first style, you can do so as:

u = ['abc', 'de', 'fghi', 'jklm', 'n', '']
v = []
for item in u:
     v.append(len(item))
print v