a = [1, 5, 2, 1, 1, 5]

def f(items):
    s = set()
    for item in items:
        if item not in s:
            yield item
            s.add(item)
print(*f(a))

def f(items, key=None):
    s = set()
    for item in items:
        val = item if key is None else key(item)
        if val not in s:
            yield item
            s.add(val)
arr = [1.1, 1.2, 2.1, 3.0]
y = f(arr, key=lambda d: sum([int(x) for x in str(d).split(".")]))
print(*y)

from string import ascii_lowercase as s
a = slice(-3, 50, 2)
x = a.indices(5)
print(s[x[0]:x[1]:x[2]])

s = "abcdef"
a = slice(-float('inf'), 1000)
print(len(s[a]))

s = "abcdef"
a = slice(-1e99, 1e99)
print(len(s[a]))

s = "abcdef"
a = slice(-10**99, 10**99)
print(s[a])

a = slice(-1000, 1100, -99)
s = "abcdef"
print(len(s[a]))

a = slice(10)
print(a.start, a.stop, a.step)

a = slice(0, 0, -1)
a.start = 1
s = "abcdef"
print(s[a])

letters = ['a', 'b', 'a', 'c', 'd', 'd', 'a']
from collections import Counter
letter_counts = Counter(letters)
top = letter_counts.most_common(2)
print(top[0][1])