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Wed Feb 18 18:12:00 EST 2004 · http://mail.python.org/pipermail/python-dev/2004-February/042602.html

[I apologize that I'm not adding this information to the bug report, but
I'm not able to log into SF right now, the login page hangs while loading]

> 1==float('nan')  (2004-02-17)
>        http://python.org/sf/899109  opened by  Arman Bostani 

I'm sure Tim can explain this better, but what happens is this: 1 is
coerced to float for comparison.  Then, the following C expression is
evaluated (Objects/floatobject.c:float_compare):
        return (i < j) ? -1 : (i > j) ? 1 : 0;
Because NaN is "unordered", 1<NaN and NaN<1 are both false, and so python
returns 0 from float_compare.  Compare to this C program:
    $ cat compare.c
    #include <stdio.h>
    #include <stdlib.h>

    int main(void) {
        double a=1.0, b = atof("nan");
        printf("a<b: %d b<a: %d a==b: %d cmp(a,b): %d\n",
                a<b, b<a, a==b, (a < a) ? -1 : (a > a) ? 1 : 0);
        return 0;
    }
    $ gcc -Wall compare.c && ./a.out nan 1.0
    a<b: 0 b<a: 0 a==b: 0 cmp(a,b): 0 

Jeff

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