How to check if a float value is a whole number
To check if a float value is a whole number, use the float.is_integer()
method:
>>> (1.0).is_integer()
True
>>> (1.555).is_integer()
False
The method was added to the float
type in Python 2.6.
Take into account that in Python 2, 1/3
is 0
(floor division for integer operands!), and that floating point arithmetic can be imprecise (a float
is an approximation using binary fractions, not a precise real number). But adjusting your loop a little this gives:
>>> for n in range(12000, -1, -1):
... if (n ** (1.0/3)).is_integer():
... print n
...
27
8
1
0
which means that anything over 3 cubed, (including 10648) was missed out due to the aforementioned imprecision:
>>> (4**3) ** (1.0/3)
3.9999999999999996
>>> 10648 ** (1.0/3)
21.999999999999996
You'd have to check for numbers close to the whole number instead, or not use float()
to find your number. Like rounding down the cube root of 12000
:
>>> int(12000 ** (1.0/3))
22
>>> 22 ** 3
10648
If you are using Python 3.5 or newer, you can use the math.isclose()
function to see if a floating point value is within a configurable margin:
>>> from math import isclose
>>> isclose((4**3) ** (1.0/3), 4)
True
>>> isclose(10648 ** (1.0/3), 22)
True
For older versions, the naive implementation of that function (skipping error checking and ignoring infinity and NaN) as mentioned in PEP485:
def isclose(a, b, rel_tol=1e-9, abs_tol=0.0):
return abs(a - b) <= max(rel_tol * max(abs(a), abs(b)), abs_tol)
You could use this:
if k == int(k):
print(str(k) + " is a whole number!")
You don't need to loop or to check anything. Just take a cube root of 12,000 and round it down:
r = int(12000**(1/3.0))
print r*r*r # 10648
We can use the modulo (%) operator. This tells us how many remainders we have when we divide x by y - expresses as x % y
. Every whole number must divide by 1, so if there is a remainder, it must not be a whole number.
This function will return a boolean, True
or False
, depending on whether n
is a whole number.
def is_whole(n):
return n % 1 == 0