Please explain collections.defaultdict(lambda: 1)

[Duncan Booth]

"metaperl.com" <metaperl at gmail.com> wrote:

> Per http://docs.python.org/lib/defaultdict-examples.html
> 
> It seems that there is a default factory which initializes each key to
> 1. So by the end of train(), each member of the dictionary model will
> have value >= 1
> 
> But why wouldnt he set the value to zero and then increment it each
> time a "feature" (actually a word) is encountered? It seems that each
> model value would be 1 more than it should be.
> 
The author explains his reasoning in the article: he wants to treat novel 
words (i.e. those which did not appear in the training corpus) as having 
been seen once.