[Tutor] Meaning of %g ?

[Sean Lee]

> > >>> print "%14.3g\n%14.3e\n%14.3f" % (bignum,bignum,bignum)
> >     1.23e+009
> >    1.235e+009
> > 1234567898.235
> >
> > But in practice, we do not know how big is the data in advance when
> > doing scientific computation in a compiled program.
>
> That is irrelevant, the format you display the data in has
> no bearing on its precision, the display format is purely to
> make it more readable.



 Another interesting one:

>>> a = 123456.78
>>> print "%g\n%e\n%f" % (a,a,a)
123457
1.234568e+005
123456.780000
>>>

Float number loses digits and becomes integer in the output ?

Can we override the %g in python, or adding in some other format identifier
so that print statement with custom format string still works ?

Here if I want to dynamically output floating data based on the number of
significant digits (SD) from an input's:

- If SD > m, truncate (or round it) in the output
- If SD < m,  just directly output the number (without padding 0 to the
end).
 - In either of above cases, similar to %g, if %e is necessary, just output
%e format as result (also truncate the data based on SD in the %e format if
necessary).

e.g, if SD = 3:
      - for input = 100.0, the output is just 100.0 (not 100.00000..), since
100.0 = 1.0 * 10e2 (2<3)
      - for input = 0.01,  the output is just 0.01, since 0.01 = 1.0 * 10e-2
(2<3)
     - for input with SD > 3,  truncate it to output.

SD can be set to some number (e.g. 6) in the program.

Thanks.
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