Counting sort and list comprehension in Python

Question

I have problem with understand how to resolve error in my code. Here it comes:

def counting_sort(some_list, max=100000):
    licznik = [0] * (max+1) 
    for x in some_list:
        licznik[x] = licznik[x]+1
    i=0
    for x in range(max+1):
        for y in range(licznik[x]):
            some_list[i]=x 
            i=i+1 
    return some_list.reverse()

def gen(number, b=100000):
    some_list = []
    return [some_list.append(random.randint(0, b)) for x in xrange(number)]

domain = [10000, 25000, 50000, 100000, 200000, 300000, 400000, 500000, 750000, 1000000]
for element in domain:
    print 'Results for: ' + str(element) + ' elements:'
    for j in range(0, 10):
        temp_list = gen(element)
        start = time.time()
        counting_sort(temp_list)
        end = time.time() - start
        print end

This is problem with line:

for x in some_list:
            licznik[x] = licznik[x]+1

I guess that it should be resolved by list comprehension, but I have no idea how to transform it this way. Any helping advice? Thanks for advance.

Answer 1

You are filling some_list with None values in your function gen. Change the line

return [some_list.append(random.randint(0, b)) for x in xrange(number)]

to:

return [(random.randint(0, b)) for x in xrange(number)]

Answer 2

Your gen function is wrong... list.append returns None and modifies somelist in place, change to:

def gen(number, b=100000):
    return [random.randint(0, b) for x in xrange(number)]

To demonstrate:

some_list = []
print [some_list.append(10) for _ in xrange(5)]
# [None, None, None, None, None]
print some_list
# [10, 10, 10, 10, 10]

And you're returning the list of Nones.

Answer 3

You are trying to use a None value as a key to the list licznik on line 5.

If you modify your Gen function to this, it should work.

def gen(number, b=100000):
    return [(random.randint(0, b)) for x in xrange(number)]