[Tutor] Best way to replace items in a list.

[Kent Johnson]

Jason Massey wrote:
> Why not:
> 
> if item in lst:
>  loc = lst.index(item)
>  lst[loc] = str

You can also just try to do the replacement and catch the ValueError 
that is raised if the item is not there:

try:
   loc = list.index(item)
   list[loc] = str
except ValueError:
   pass

If lst is long this will be faster because it only searches lst for item 
once. If lst is short maybe the first version is better because the code 
is shorter.

This is an example of two different approaches to handling exceptional 
conditions: Look Before You Leap versus Easier to Ask Forgiveness than 
Permission. In LBYL you check for the exceptional condition early, so 
you avoid exceptions. In EAFP you proceed as if something is sure to 
work and clean up after if you were wrong.

In many cases EAFP produces code that makes fewer assumptions about its 
environment and is more suited to Python's dynamic style. In this simple 
case it doesn't make any difference.

By the way don't use 'list' as the name of a variable (or 'file', 
'dict', 'set' or 'str'), they are all the names of built-in types in 
Python and using them as variable names will hide the built-in name.

Kent