List comprehensions' ugliness (Was: Re: How to explain exactly what "def" does?)

[Duncan Booth]

Donnal Walter <donnal at donnal.net> wrote in 
news:mailman.1044525858.22549.python-list at python.org:

>> mylist.extend(otherlist) is better.
>> 
> 
> mylist = mylist + otherlist
> 
> The above assignment statement is an idiom that I have (perhaps naively) 
> adopted. Is the .extend syntax more efficient? I can also see where it 
> might be considered more readable or more accurate. (?)

Note that these do different things:

mylist.extend(otherlist)
 modifies mylist in place, so any other reference to mylist will also see 
the new value. This may be more efficient if mylist doesn't have to be 
copied (although increasing its size is still likely to involve a copy 
somewhere), but it can have unwanted side effects.

mylist = mylist + otherlist
 creates a new list so other references to the object are not affected.

mylist += otherlist
 is the same as the former if mylist is of type list, but other sequences 
may regard it as the same as the latter.

-- 
Duncan Booth                                             duncan at rcp.co.uk
int month(char *p){return(124864/((p[0]+p[1]-p[2]&0x1f)+1)%12)["\5\x8\3"
"\6\7\xb\1\x9\xa\2\0\4"];} // Who said my code was obscure?