Codeacademy上的python数学除以int与float时表现怪异。 动态类型/广播问题

Question

Ok so the problem asks to find the median(middle number) in a list of numbers. If the list has an even amount of numbers return the average of the two middle numbers.

I came across some code doesn't work on the site but does in PyCharm. I imagine it is because some of the code on code academy's learning python is old (for example their print function and raw_input() are now deprecated)

The below does not work on CodeAcademy

def median(ls):
    ls = sorted(ls)
    length = len(ls)
    median = 0.0
    temp = 0

    if length % 2 == 0:
        temp = int(length / 2)
        median = float (ls[temp-1] + ls[temp]) / 2 #why is this a problem?
        return median
    else:
        temp=int((length-1) / 2)
        median = ls[temp]
        return median

Note: the above returns 4.0 instead of 4.5 when passed [4,5,5,4]

however when I change the /2 to /2.0 like below it works.

def median(ls):
    ls = sorted(ls)
    length = len(ls)
    median = 0.0
    temp = 0

    if length % 2 == 0:
        temp = int(length / 2)
        median = float (ls[temp-1] + ls[temp]) / 2.0 #here
        return median
    else:
        temp=int((length-1) / 2)
        median = ls[temp]
        return median

Note: the above correctly returns 4.5 when passed [4,5,5,4]

So even though I've figured out how to solve the problem, I want to know why it happened in the event that even though both code examples work in newer versions of python, is one is more correct or 'cleaner' and why?

Answer 1

Ok so what I believe happened in the first code example that was returning weird results is that Python casted the first two numbers to ints in order to divide by int (yielding 4 when passed [4,4,5,5] (after sorting)) and then casted that answer (4) to a float giving 4.0. but when I divided by 2.0 it casted those numbers to floats first giving the correct 4.5. This also allowed me to remove the explicit cast to float and when tested worked on code academy