Creating a List of Empty Lists

[Duncan Booth]

michael at foord.net (Fuzzyman) wrote in 
news:8089854e.0312040649.4a7f1715 at posting.google.com:

> I eventually discovered that (as a silly example) :
> a = [[]]*10
> b=-1 
> while b < 10:
>     b += 1
>     a[b] = b
> print a 
> 
> Produced :
> [ [9], [9], [9]......
> 
> Which isn't at all what I intended...............
> What is the correct, quick way of doing this (without using a loop and
> appending...) ?

The recommended way these days is usually:

    a = [ [] for i in range(10) ]

That still has a loop and works by appending empty lists, but at least its 
just a single expression. Also you can incorporate the next stage of your 
initialisation quite easily:

    a = [ [b] for b in range(10) ]

-- 
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?