(no) fast boolean evaluation ? missing NOT

[Bruno Desthuilliers]

Stef Mientki a écrit :
(snip)
> Gabriel: you pointed me to this page:
> The exact behavior is defined in the Language Reference 
> <http://docs.python.org/ref/Booleans.html>
> 
> <quote>
> or_test      ::=      and_test | or_test "or" and_test
> </quote
> 
> Can you imagine, while I'm not a programmer, just a human,
> that I don't understand one bit of this line.

This is a variant[2] of the BNF notation[1] for languages grammar. 
You'll find such notation in almost any programming language.

[1] http://en.wikipedia.org/wiki/Backus-Naur_form
[2] http://docs.python.org/ref/notation.html

> So now I'm left with just one question:
> for bitwise operations I should use &, |, ^

yes.

> for boolean operations I should use and, or, xor

yes.

> but after doing some test I find strange effects:
>  >>> A = 4
>  >>> B = 5
>  >>> A and B
> 5
>  >>> A & B
> 4
>  >>> A or B
> 4
>  >>> A | B
> 5


Nothing strange here. You now know how boolean operators works. Bitwise 
operators are something different (while still related). Represent 
yourself ints as bit fields, ie (restricting ourselves to 4-bits words 
for the example):

0 => 0000
1 => 0001
2 => 0010
3 => 0011
4 => 0100
5 => 0101
6 => 0110
7 => 0111
8 => 1000

(etc)

The bitwise operators works this way:

1/ the & operator compares each bit of it's operands, and for each 
returns '1' if both bits are '1', else '0'. So you have:

A & B => 4 & 5 => 0100 & 0101 => 0100 => 4

   0100
& 0101
   ----
   0100

2/ the | operator compares each bit of it's operands, and for each 
returns '1' if one of the bits is '1', else '0'. So you have:

A | B => 4 | 5 => 0100 | 0101 => 0101 => 5

   0100
| 0101
   ----
   0101


HTH