Why doesn't Python have a sign function?

Question

I can\'t understand why Python doesn\'t have a sign function. It has an abs builtin (which I consider sign\'s sister), but no si

Answer 1

Yes a correct sign() function should be at least in the math module - as it is in numpy. Because one frequently needs it for math oriented code.

But math.copysign() is also useful independently.

cmp() and obj.__cmp__() ... have generally high importance independently. Not just for math oriented code. Consider comparing/sorting tuples, date objects, ...

The dev arguments at http://bugs.python.org/issue1640 regarding the omission of math.sign() are odd, because:

• There is no separate -NaN
• sign(nan) == nan without worry (like exp(nan) )
• sign(-0.0) == sign(0.0) == 0 without worry
• sign(-inf) == -1 without worry

-- as it is in numpy