[Python-Dev] Mixing float and Decimal -- thread reboot (original) (raw)

Mark Dickinson dickinsm at gmail.com
Mon Mar 22 21:12:27 CET 2010

On Mon, Mar 22, 2010 at 8:02 PM, Pierre B. <pierrebai at hotmail.com> wrote:

Sorry to intervene out of the blue, but I find the suggested rule for fractional to decimal conversion not as clean as I'd expect.

If fractions are converted to decimals when doing arithmetics, would it be worthwhile to at least provide a minimum of fractional conversion integrity? What I have in mind is the following rule: When doing conversion from fraction to decimal, always generate a whole number of repeating digits, always at least twice. Examples, with a precision of 5 in Decimal: 1/2 -> 0.50000 1/3 -> 0.33333 1/11 -> 0.090909 # Note that we produced 6 digits, because # the repeating pattern contains 2 digits. 1/7 -> 0.142857142857  # Always at least two full patterns.

And for 1/123123127? The decimal expansion of this fraction has a period of over 15 million!

Sorry, but this doesn't seem like a feasible or desirable strategy.

Mark

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