Representing fractions (was: Help me with this code)
Ben Finney
ben+python at benfinney.id.au
Wed Nov 6 03:06:41 CET 2013
chovdary at gmail.com writes:
> def sequence_b(N):
> N = 10
> result = 0
> for k in xrange (1,N):
> result += ((-1) ** (k+1))/2*k-1
Every number here is an integer. Python 2 will keep all the computations
integers by default::
$ python2
>>> 1 / 2
0
You want to use Python 3, which does “true division” by default::
$ python3
>>> 1 / 2
0.5
> But i want output as
> 1
> -1/3
> 1/5
> -1/7
> 1/9
> -1/11
> 1/13
> -1/15
> 1/17
> -1/19
You're not going to get that output from Python built-in number types.
If you want numbers which represent fractions (as opposed to integers,
or decimal numbers, or floating-point numbers), you want the ‘fractions’
module <URL:http://docs.python.org/3/library/fractions.html> which will
represent the number explicitly with numerator and denominator::
$ python3
>>> import fractions
>>> result = fractions.Fraction(1) / fractions.Fraction(2)
>>> result
Fraction(1, 2)
>>> print(result)
1/2
--
\ “A hundred times every day I remind myself that […] I must |
`\ exert myself in order to give in the same measure as I have |
_o__) received and am still receiving” —Albert Einstein |
Ben Finney
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