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 2 in the following?
c = a / b
Answers:
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Method 1
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 __future__.
>>> from __future__ import division >>> a = 4 >>> b = 6 >>> c = a / b >>> c 0.66666666666666663
Method 2
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.
Method 3
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.
>>> 1/2 0.5
Floor division, the classic division behavior for integers, is now a // b:
>>> 1//2 0 >>> 1//2.0 0.0
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 division >>> 1/2 0.5 >>> 1//2 0 >>> 1//2.0 0.0
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 module 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) 0.5 >>> 1 / 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
Method 4
c = a / (b * 1.0)
Method 5
In Python 3.x, the single slash (/) always means true (non-truncating) division. (The // operator is used for truncating division.) In Python 2.x (2.2 and above), you can get this same behavior by putting a
from __future__ import division
at the top of your module.
Method 6
Just making any of the parameters for division in floating-point format also produces the output in floating-point.
Example:
>>> 4.0/3 1.3333333333333333
or,
>>> 4 / 3.0 1.3333333333333333
or,
>>> 4 / float(3) 1.3333333333333333
or,
>>> float(4) / 3 1.3333333333333333
Method 7
Add a dot (.) to indicate floating point numbers
>>> 4/3. 1.3333333333333333
Method 8
This will also work
>>> u=1./5 >>> print u 0.2
Method 9
If you want to use “true” (floating point) division by default, there is a command line flag:
python -Q new foo.py
There are some drawbacks (from the PEP):
It has been argued that a command line option to change the
default is evil. It can certainly be dangerous in the wrong
hands: for example, it would be impossible to combine a 3rd
party library package that requires -Qnew with another one that
requires -Qold.
You can learn more about the other flags values that change / warn-about the behavior of division by looking at the python man page.
For full details on division changes read: PEP 238 — Changing the Division Operator
Method 10
from operator import truediv c = truediv(a, b)
Method 11
from operator import truediv c = truediv(a, b)
where a is dividend and b is the divisor.
This function is handy when quotient after division of two integers is a float.
All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0