python codewars, Python 3

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#python 3.5.2

print("# ------------------ #")
print("Count the unique duplicates")

ss = None
def check_dup():
    if ss is None: return 0
    elems = [i for i in ss.lower() if ss.count(i) != 1]
    count = len(list(set(elems))) 
    return count

print (check_dup())

print("\n")
   
        
print("# ------------------ #")
print("Make a program that filters a list of strings and returns a list with only your friends name in it.")

print("If a name has exactly 4 letters in it, you can be sure that it has to be a friend of yours!")
print("Otherwise, you can be sure he's not...")

print('Ex: Input = ["Ryan", "Kieran", "Jason", "Yous"], Output = ["Ryan", "Yous"] ')

print("Note: keep the original order of the names in the output")

peoples = ["Ryan", "Kieran", "Jason", "Yous"]

def friend(x):
    return list(filter(lambda y: len(y) == 4, x))

print(friend(peoples))
        
        
print("\n")
 
        
print("# ------------------ #")
print("Given a set of numbers, return the additive inverse of each.") 
print("Each positive becomes negatives, and the negatives become positives.")
        
print("invert([1,2,3,4,5]) == [-1,-2,-3,-4,-5]")
print("invert([1,-2,3,-4,5]) == [-1,2,-3,4,-5]")
print("invert([]) == []")

nums = [1, -2, 3, -4, 5]

def invert(lst):
    return [-i for i in lst]

print(invert(nums))

print("\n")

# ------------------ #

print('The new "Avengers" movie has just been released!')
print("There are a lot of people at the cinema box office standing in a huge line. ")
print('Each of them has a single 100, 50 or 25 dollars bill. An "Avengers" ticket costs 25 dollars.')

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Absolute running time: 0.13 sec, cpu time: 0.09 sec, memory peak: 6 Mb, absolute service time: 0,14 sec