[Tutor] Replacement of items in a list

Fri, 3 Aug 2001 15:09:04 -0400

On Fri, Aug 03, 2001 at 12:30:52PM -0600, VanL wrote:
| Why is this?
| 
| :::::::::::::: Begin test.py
| 
| #!/usr/bin/env python
| 
| import string
| 
| lst = ['ONE', 'TWO', 'THREE']
| lst1 = lst[:]
| lst2 = lst[:]
| 
| def replace1(list):
|     """ Uses item replacement"""
|     for x in list:

The for loop is just a shorthand notation for (except that you have no
access to the 'i')

try :
    i = 0
    while 1 :
        x = list[i]
        i+=1
        <body>
except IndexError : pass

So what you have as the variable 'x' is a reference to an item in the
list.  The list is irrelevant in this function, except as a convenient
way to get to all the various x's

|         x = string.lower(x)

Here you change your local variable 'x' to refer to a new string, but
you haven't touched the list at all.

| def replace2(list):
|     """Uses position replacement"""
|     for x in range(len(list)):
|         list[x] = string.lower(list[x])

This works because you have modified the list as opposed to simply
adjusting a local reference.

HTH,
-D