python float to string without precision loss

Question

For python 3 I want to convert a float to a string, with possibly different length (i.e. number of digits) but with full precision.

Also I need to have a decimal point in any case:

1    -> '1.'
1/10 -> '0.1000000000000000055511151231257827021181583404541015625'

currently my code is this:

from decimal import Decimal
def formatMostSignificantDigits(x):
    out = str(Decimal(x))
    if out.find('.') < 0:
        out += '.'
    return out

can this be done more elegantly? (e notation would be possible, too)

I mean, I would use endswith instead of .find < 0, but other than that it looks fine. This would probably be better for codereview, as "more elegantly" isn't really something objective that we can give you. — Morgan Thrapp

ands ands · Accepted Answer · 2016-06-27T14:57:14

why do you use Decimal, you can just use:

x = 0.1
s = str(x)
print(s)   # this prints '0.1'

but if you use Decimal for something else than instead of this:

out = str(Decimal(x))
if out.find('.') < 0:
    out += '.'
return out

you can just use:

return Decimal(x).__str__()

Edit 1:

also good module for float precision is bigfloat:

from bigfloat import BigFloat
x = 0.1
print(BigFloat(x, precision(300)).__str__())
# thsi will print'0.10000000000000000555111512312578270211815834045410156250000000000000000000000000000000000000'
# but if you use this:
print(BigFloat(x.__str__(), precision(300)).__str__())
# it can be precise as much as you want
print(BigFloat(x.__str__(), precision(100000)).__str__()) # try this

python float to string without precision loss

2 Answers