Easy way of finding decimal places
"the number of decimal places" is not a property a floating point number has, because of the way they are stored and handled internally.
You can get as many decimal places as you like from a floating point number. The question is how much accuracy you want. When converting a floating point number to a string, part of the process is deciding on the accuracy.
Try for instance:
1.1 - int(1.1)
And you will see that the answer is:
0.10000000000000009
So, for this case, the number of decimals is 17. This is probably not the number you are looking for.
You can, however, round the number to a certain number of decimals with "round":
round(3.1415 - int(3.1415), 3)
For this case, the number of decimals is cut to 3.
You can't get "the number of decimals from a float", but you can decide the accuracy and how many you want.
Converting a float to a string is one way of making such a decision.
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
The negation of the exponent is the number of digits after the decimal point, unless the exponent is greater than 0
.