Something Wrong On My python :float() argument must be a string or a number

Question

I am right now a Python newcomer, and I study this by finishing courses on http://www.codecademy.com. This website offers an online judge system just like an ACM to exam if my code works fine. And it works great on my others code except this one.

I tried to copy this code to my local pc with Python 2.6 installed and it works.

By the way, can you suggest some Python grammar books to a beginner like me, I just want to know a little inner detail about this language...

Because I cannot post a picture here I just paste the code below:

on my mac: :

    [~ tk$]cat test8.py 
def median(li):

    if len(li) >= 2:
        li_test = sorted(li)
        if len(li_test)%2 == 0:
            cd1 = len(li_test)/2-1
            cd2 = cd1 
            re = (li_test[cd1] + li_test[cd2])/2.0
        else:
            cd = (len(li_test)+1)/2-1
            re = li_test[cd]
    else:
        re = li
    return re
print median([1,2,3])

[~ tk$]python test8.py 

2

[~ tk$]

on the websites: the title is : Practice makes perfect 15/15:

def median(li):

    if len(li) >= 2:
        li_test = sorted(li)
        if len(li_test)%2 == 0:
            cd1 = len(li_test)/2-1
            cd2 = cd1 
            re = (li_test[cd1] + li_test[cd2])/2.0
        else:
            cd = (len(li_test)+1)/2-1
            re = li_test[cd]
    else:
        re = li
    return re


Oops, try again. Your function crashed on [1] as input because your function throws a "float() argument must be a string or a number" error.

petabyte · Accepted Answer · 2014-03-06 05:21:12Z

1

else:
    re = li

The error is occurring because if the length of li is 1 or 0, then you are returning the list li.

>>> median([1])
[1]
>>> median([0])
[0]

Maybe you want

if len(li) >= 1:
  ...
else:
    raise IndexError("No items in this list")

Another bug in your code is if there are even number of elements in the list, you should take the average of the two middle elements. But in your code,

    if len(li_test)%2 == 0:
        cd1 = len(li_test)/2-1
        cd2 = cd1 
        re = (li_test[cd1] + li_test[cd2])/2.0

You take one of the two middle elements, and add the same number twice and divide by two. It should be

    if len(li_test) % 2 == 0:
        cd1 = len(li_test) / 2
        cd2 = cd1 - 1
        re = (li_test[cd1] + li_test[cd2])/2.0

edited Mar 6, 2014 at 5:21

answered Mar 6, 2014 at 4:53

petabyte

1,5974 gold badges17 silver badges34 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

tk_y1275963 Over a year ago

No, I don't think I can do that. It is a online judge system, So I can only make my codes to satisfy its criterion. In the case thatthe length of [1] is 1, clearly the median number is 1 so I just returned the number. I can't see the mistake.

petabyte Over a year ago

You are returning the list [1] not the int 1

Chris Johnson Over a year ago

TK, to illustrate Jay's second point -- what is the median of [1,3]?

tk_y1275963 Over a year ago

Sorry, I am just being busy with my Classes.. I know where my fault is already.[0] and 0 is not the same thing. Sorry I used to be a Matlab user and those two are pretty confusing. It looks I need some more practices. Thanks for your guys help.

Collectives™ on Stack Overflow

Something Wrong On My python :float() argument must be a string or a number

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related