Lisp to Python translation criticism?

Sean 'Shaleh' Perry shalehperry at attbi.com
Sat Aug 17 04:58:26 CEST 2002


On 17-Aug-2002 John E. Barham wrote:
> Don't know how many saw the story on Slashdot about Paul Graham's article
> (http://www.paulgraham.com/spam.html) on how he filters spam.  He posted two
> snippets of code in Lisp, a language which I only have a very passing
> knowledge of.  Here's my attempt at translating it into Python:
> 

I was pondering this myself (-:

> Python:
> 
> def spam_word_prob(word, good, bad, ngood, nbad):
>     g = 2 * good.get(word, 0)
>     b = bad.get(word, 0)
>     if g + b >= 5:
>         return max(0.01, min(0.99, float(min(1, b / nbad) / ((min(1, g /
> ngood) + min(1, b / nbad))))))
>     else:
>         return 0.0
> 

one word variable names are rough on the reader.  I would also probably factor
that return statement into smaller statements if possible.

> def spam_prob(probs):
>     prod = 1.0
>     for prob in probs:
>         prod = prod * prob

prod = reduce(lambda x,y: x * y, probs)

or

import operator
prod = reduce(operator.mul, probs) # for those who dislike lambda (-:

Personally, I would do this closer to the use of prod.  It looks like you mean
to use it but only use it in the last two lines.

>     inv_probs = [1 - x for x in probs]
>     inv_prob = 1.0
>     for prob in inv_probs:
>         inv_prob = inv_prob * prob
>     return prod / (prob + inv_prob)
> 
> Any comments on the correctness, style, efficiency etc. of my translation?
> I'd like to write a Python spam filtering system using Graham's techniques.
> 

I was pondering doing this and then using a pickle to retrieve the tables. 
What were you considering?





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