How can I force division to be floating point? Division keeps rounding down to 0?
In Python 2, division of two ints produces an int. In Python 3, it produces a float. We can get the new behaviour by importing from
from __future__ import division a = 4b = 6c = a / b c0.66666666666666663
You can cast to float by doing
c = a / float(b). If the numerator or denominator is a float, then the result will be also.
A caveat: as commenters have pointed out, this won't work if
b might be something other than an integer or floating-point number (or a string representing one). If you might be dealing with other types (such as complex numbers) you'll need to either check for those or use a different method.
How can I force division to be floating point in Python?
I have two integer values a and b, but I need their ratio in floating point. I know that a < b and I want to calculate a/b, so if I use integer division I'll always get 0 with a remainder of a.
How can I force c to be a floating point number in Python in the following?
c = a / b
What is really being asked here is:
"How do I force true division such that
a / b will return a fraction?"
Upgrade to Python 3
In Python 3, to get true division, you simply do
a / b.
Floor division, the classic division behavior for integers, is now
a // b:
However, you may be stuck using Python 2, or you may be writing code that must work in both 2 and 3.
If Using Python 2
In Python 2, it's not so simple. Some ways of dealing with classic Python 2 division are better and more robust than others.
Recommendation for Python 2
You can get Python 3 division behavior in any given module with the following import at the top:
from __future__ import division
which then applies Python 3 style division to the entire module. It also works in a python shell at any given point. In Python 2:
from __future__ import division1/20.51//201//2.00.0
This is really the best solution as it ensures the code in your module is more forward compatible with Python 3.
Other Options for Python 2
If you don't want to apply this to the entire module, you're limited to a few workarounds. The most popular is to coerce one of the operands to a float. One robust solution is
a / (b * 1.0). In a fresh Python shell:
1/(2 * 1.0)0.5
Also robust is
truediv from the
operator.truediv(a, b), but this is likely slower because it's a function call:
from operator import truediv truediv(1, 2)0.5
Not Recommended for Python 2
Commonly seen is
a / float(b). This will raise a TypeError if b is a complex number. Since division with complex numbers is defined, it makes sense to me to not have division fail when passed a complex number for the divisor.
1 / float(2)0.51 / float(2j)Traceback (most recent call last): File "<stdin>", line 1, in <module>TypeError: can't convert complex to float
It doesn't make much sense to me to purposefully make your code more brittle.
You can also run Python with the
-Qnew flag, but this has the downside of executing all modules with the new Python 3 behavior, and some of your modules may expect classic division, so I don't recommend this except for testing. But to demonstrate:
$ python -Qnew -c 'print 1/2'0.5$ python -Qnew -c 'print 1/2j'-0.5j