dictionary initialization

[Jeffrey Froman]

Weiguang Shi wrote:

> With awk, I can do something like
> $ echo 'hello' |awk '{a[$1]++}END{for(i in a)print i, a[i]}'
> 
> That is, a['hello'] was not there but allocated and initialized to
> zero upon reference.
> 
> With Python ... <snip>
> I have to initialize b[1] explicitly in the first place.

You could use the dictionary's setdefault method, if your value is mutable:

>>> b={}
>>> for n in xrange(100):
...     b.setdefault('foo', [0])[0] += 1
... 
>>> b['foo'][0]
100

   Jeffrey