[Python-Dev] PROPOSAL: exposure of values in limits.h and float.h (original) (raw)

Trent Mick trentm@activestate.com
Tue, 2 May 2000 16:03:22 -0700

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I apologize if I am hitting covered ground. What about a module (called limits or something like that) that would expose some appropriate #define's in limits.h and float.h.

For example:

limits.FLT_EPSILON could expose the C DBL_EPSILON limits.FLT_MAX could expose the C DBL_MAX limits.INT_MAX could expose the C LONG_MAX (although that particulay name would cause confusion with the actual C INT_MAX)

• Does this kind of thing already exist somewhere? Maybe in NumPy.

• If we ever (perhaps in Py3K) turn the basic types into classes then these could turn into constant attributes of those classes, i.e.: f = 3.14159 f.EPSILON = <as set by C's DBL_EPSILON>

• I thought of these values being useful when I thought of comparing two floats for equality. Doing a straight comparison of floats is dangerous/wrong but is it not okay to consider two floats reasonably equal iff: -EPSILON < float2 - float1 < EPSILON Or maybe that should be two or three EPSILONs. It has been a while since I've done any numerical analysis stuff.

  I suppose the answer to my question is: "It depends on the situation." Could this algorithm for float comparison be a better default than the status quo? I know that Mark H. and others have suggested that Python should maybe not provide a float comparsion operator at all to beginners.

Trent

-- Trent Mick trentm@activestate.com

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