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From: Roy Smith <roy@panix.com>
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Date: Mon, 28 Apr 2014 12:00:23 -0400
Subject: Significant digits in a float?
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Xref: csiph.com comp.lang.python:70682

I'm using Python 2.7

I have a bunch of floating point values.  For example, here's a few =
(printed as reprs):

38.0
41.2586
40.75280000000001
49.25
33.795199999999994
36.837199999999996
34.1489
45.5

Fundamentally, these numbers have between 0 and 4 decimal digits of =
precision, and I want to be able to intuit how many each has, ignoring =
the obvious floating point roundoff problems.  Thus, I want to map:

38.0  =3D=3D> 0
41.2586 =3D=3D> 4
40.75280000000001 =3D=3D> 4
49.25 =3D=3D> 2
33.795199999999994 =3D=3D> 4
36.837199999999996 =3D=3D> 4
34.1489 =3D=3D> 4
45.5 =3D=3D> 1

Is there any clean way to do that?  The best I've come up with so far is =
to str() them and parse the remaining string to see how many digits it =
put after the decimal point.

The numbers are given to me as Python floats; I have no control over =
that.  I'm willing to accept that fact that I won't be able to =
differentiate between float("38.0") and float("38.0000").  Both of those =
map to 1, which is OK for my purposes.

---
Roy Smith
roy@panix.com