CODEWITHSUNDEEP
pythonpython-2.7
macavity
macavity

Reputation: 427

Python sort method is not working inside the user defined function

Can anyone please tell whats wrong with this code? I need to output the sorted list and the reverse list

def sort_num():
    count=1;
    global a
    a=[]
    while count<11:
        no=int(raw_input("no %d:" %count))
        a.append(no)
        count+=1
    print a
    print a.reverse()
    print a.sort()

and my output is:

[2, 33, 4, 11, 7, 8, 5, 6, 33, 0]
None
None

Upvotes: 2

Views: 10388

Answers (4)

James Sapam
James Sapam

Reputation: 16940

Bit explanation about why list.sort() doesn't return the sorted list?

In situations where performance matters, making a copy of the list just to sort it would be wasteful. Therefore, list.sort(), sorts the list in place.

In order to remind you of that fact, it does not return the sorted list. This way, you won’t be fooled into accidentally overwriting a list when you need a sorted copy but also need to keep the unsorted version around. In that case use builtin sorted() function.

sorted() is a built-in function:

>>> help(sorted)
Help on built-in function sorted in module __builtin__:

sorted(...)
    sorted(iterable, cmp=None, key=None, reverse=False) --> new sorted list

>>>

list.sort() is a method of list which will change on the list itself:

>>> help(list.sort)
Help on method_descriptor:

sort(...)
    L.sort(cmp=None, key=None, reverse=False) -- stable sort *IN PLACE*;
    cmp(x, y) -> -1, 0, 1

Snippet:

>>> ls = [3,2,1]
>>> sorted(ls)
[1, 2, 3]
>>> ls
[3, 2, 1]
>>> ls.sort()
>>> ls
[1, 2, 3]
>>>

Hope that will clear your doubt.

Upvotes: 2

Jitendra Pareek
Jitendra Pareek

Reputation: 637

This will give you a sorted version of the array.

sorted(a, reverse=True)

If you want to sort in-place:

a.sort(reverse=True)

Upvotes: 1

Samuel
Samuel

Reputation: 1374

Another option is to call the builtin reversed (returns an iterator) and sorted (returns a sorted copy) methods.

print list(reversed(a))
print sorted(a)

Upvotes: 1

thefourtheye
thefourtheye

Reputation: 239453

list.reverse and list.sort are inplace reversing and sorting functions. They return None. So, you have to print a separately, like this

a.reverse()
print a
a.sort()
print a

Upvotes: 5

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