Arbitrary precision floats are needed to properly answer this question. Therefore using the decimal module is a must. There is no method to convert a decimal to a string without ever using the exponential format (part of the original question), so I wrote a function to do just that:
def removeExponent(decimal):
digits = [str(n) for n in decimal.as_tuple().digits]
length = len(digits)
exponent = decimal.as_tuple().exponent
if length <= -1 * exponent:
zeros = -1 * exponent - length
digits[0:0] = ["0."] + ["0"] * zeros
elif 0 < -1 * exponent < length:
digits.insert(exponent, ".")
elif 0 <= exponent:
digits.extend(["0"] * exponent)
sign = []
if decimal.as_tuple().sign == 1:
sign = ["-"]
print "".join(sign + digits)
The problem is trying to round to significant figures. Decimal's "quantize()" method won't round higher than the decimal point, and the "round()" function always returns a float. I don't know if these are bugs, but it means that the only way to round infinite precision floating point numbers is to parse it as a list or string and do the rounding manually. In other words, there is no sane answer to this question.
