Question

Is there an easy way or integrated function to find out the decimal places of a floating point number?

The number is parsed from a string, so one way is to count the digits after the . sign, but that looks quite clumsy to me. Is there a possibility to get the information needed out of a float or Decimal object?

Answer 1

To repeat what others have said (because I had already typed it out!), I’m not even sure such a value would be meaningful in the case of a floating point number, because of the difference between the decimal and binary representation; often a number representable by a finite number of decimal digits will have only an infinite-digit representation in binary.

In the case of a decimal.Decimal object, you can retrieve the exponent using the as_tuple method, which returns a namedtuple with sign, digits, and exponent attributes:

>>> d = decimal.Decimal('56.4325')
>>> d.as_tuple().exponent
-4

>>> d = decimal.Decimal('56.43256436')
>>> d.as_tuple().exponent
-8

>>> d = decimal.Decimal(str(56.4325))
>>> d.as_tuple().exponent
-4

The negation of the exponent is the number of digits after the decimal point, unless the exponent is greater than 0.