string - Python float - str - float weirdness

Question

>>> float(str(0.65000000000000002))

0.65000000000000002

>>> float(str(0.47000000000000003))

0.46999999999999997     ???

What is going on here? How do I convert 0.47000000000000003 to string and the resultant value back to float?

I am using Python 2.5.4 on Windows.

Answer 1

str(0.47000000000000003) give '0.47' and float('0.47') can be 0.46999999999999997. This is due to the way floating point number are represented (see this wikipedia article)

Note: float(repr(0.47000000000000003)) or eval(repr(0.47000000000000003)) will give you the expected result, but you should use Decimal if you need precision.