[Tutor] Division operation

[Terry Carroll]

On Tue, 16 May 2006, Miguel Estrada wrote:

> def function():
>     x = int(raw_input("Enter value of x: "))
>     y = int(raw_input("Enter value of y: "))
>     z = x / y
>     print "The value of z is", z, "unit of measurement"
> 
> 
> Now, say, user input:
> 
> x = 200
> y = 1000
> 
> The value returned will be '0'.
> 
> My question: What is the proper way of writing the operation so that if
> z = x /y, the result would be '0.20' instead of just '0'?

This is a frustrating design choice in Python, which I believe is on the 
list of Guido's regrets and will be corrected in Python 3.0.

Where both operands are integers, Python division truncates to and integer 
result, thus:

>>> x = 200
>>> y = 1000
>>> z = x/y
>>> z
0

But if either operand is a float, you get the results that you'd expect:

>>> x = 200.0
>>> y = 1000
>>> z = x/y
>>> z
0.20000000000000001
>>>

(the "000000..1" is rounding error from the basic impossibility of 
representing 1/5 in a binary system)

You can include the following in your program (I often do) if you want 
division to operate the way you expect:

>>> from __future__ import division

>>> from __future__ import division
>>> x = 200
>>> y = 1000
>>> z = x/y
>>> z
0.20000000000000001
>>>