unusual exponential formatting puzzle

[Neal Becker]

mensanator at aol.com wrote:

> 
> mensanator at aol.com wrote:
>> Neal Becker wrote:
>> > Like a puzzle?  I need to interface python output to some strange old
>> > program.  It wants to see numbers formatted as:
>> >
>> > e.g.: 0.23456789E01
>> >
>> > That is, the leading digit is always 0, instead of the first
>> > significant
>> > digit.  It is fixed width.  I can almost get it with '% 16.9E', but not
>> > quite.
>> >
>> > My solution is to print to a string with the '% 16.9E' format, then
>> > parse it
>> > with re to pick off the pieces and fix it up.  Pretty ugly.  Any better
>> > ideas?
>>
>> If you have gmpy available...
>>
>> >>> import gmpy
>>
>> ...and your floats are mpf's...
>>
>> >>> s = gmpy.pi(64)
>> >>> s
>> mpf('3.14159265358979323846e0',64)
>>
>> ...you can use the fdigits function
>>
>> >>> t = gmpy.fdigits(s,10,8,0,0,2)
>>
>> ...to create a seperate digit string and exponent...
>>
>> >>> print t
>> ('31415927', 1, 64)
>>
>> ...which can then be printed in the desired format.
>>
>> >>> print "0.%sE%02d" % (t[0],t[1])
>> 0.31415927E01
> 
> Unless your numbers are negative.
> 
>>>> print "0.%sE%02d" % (t[0],t[1])
> 0.-31415927E03
> 
> Drat. Needs work.
> 
> 
> 
> And does the format permit large negative exponents (2 digits + sign)?
> 

I think the abs (exponent) < 10 for now

>>>> print "0.%sE%02d" % (t[0],t[1])
> 0.31415927E-13
>