[Tutor] Do something on list elements
alan.gauld at yahoo.co.uk
Fri Jul 27 19:24:41 EDT 2018
On 27/07/18 23:32, Cameron Simpson wrote:
>> for index, s in l:
>> l[index] = s.replace('X','')
> I think you meant:
> for index, s in enumerate(l):
Oops, yes. Sorry.
>> In Python you very rarely need to resort to using indexes
>> to process the members of a collection. And even more rarely
>> do you need to manually increment the index.
> I use indices when I need to modify the elements of a list in place.
Yes, that's probably the most common use case, and
enumerate is the best way to do that.
> comprehension makes a shiny new list. That is usually fine, but not always what
> is required.
>From a purist point of view its usually preferable but in
practice making copies of large data structures is usually
a bad idea. In that case you are forced to resort to
enumerate, I agree.
> The other place I use enumerate in a big way is to track line numbers in files,
> as context for error messages (either now or later). For example:
Yes, but then you don't use the index to access/process
the data. Its just providing context.
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