Euler #26, how to convert rational number to string with better precision?

Question

I want to get 1/7 with better precision, but it got truncated. How can I get better precision when I convert a rational number?

>>> str(1.0/7)[:50]
'0.142857142857'

Answer 1

Python has a built-in library for arbitrary-precision calculations: Decimal. For example:

>>>from decimal import Decimal, getcontext
>>>getcontext().prec = 50
>>>x = Decimal(1)/Decimal(7)
>>>x
Decimal('0.14285714285714285714285714285714285714285714285714')
>>>str(x)
'0.14285714285714285714285714285714285714285714285714'

Look at the Python Decimal documentation for more details. You can change the precision to be as high as you need.

Answer 2

You could multiply the numerator by a large 10^N and stick with arbitrary-precision integers.

EDIT

i mean:

> def digits(a,b,n=50): return a*10**n/b
.
> digits(1,7)
14285714285714285714285714285714285714285714285714L

Python's integers are arbitrary precision. Python's floats are never arbitrary precision. (you'd have to use Decimal, as another answer has pointed out)