Bayes Theorem in Python

David C. Ullrich ullrich at
Tue May 22 18:55:53 CEST 2001

On Tue, 22 May 2001 14:26:14 +0200, "Alex Martelli"
<aleaxit at> wrote:

>"Ron Stephens" <rdsteph at> wrote in message
>news:3B08F864.CD9EA4FB at
>> Does anyone know if someone has already coded Bayes theorem into Python?
>You mean as in:
>def Bayes(P_H, P_E, P_E_given_H):
>    P_H_given_E = (P_H * P_E_given_H) / P_E
>    return P_H_given_E

That's not a coding of Bayes' theorem in Python, it's a coding
of an application of Bayes' theorem. A coding of Bayes's
theorem would look more like this:

Bayes_Theorem = '''If E and H are events in a probability space
and P(E) > 0 then

    P(H|E) = P(H) P(E|H) / P(E).'''

A lot easier to code in Python than in a lot of languages...

>...?  I suspect somebody must have already coded one
>multiplication and one division into one Python expression,
>yes, although it's hard to be sure about the variable
>names they may have chosen.  Or do you mean something
>completely different...?

David C. Ullrich
"Sometimes you can have access violations all the
time and the program still works." (Michael Caracena,
comp.lang.pascal.delphi.misc 5/1/01)

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