def f(seq):
    if not seq:
        yield seq
    else:
        for i in range(len(seq)):
            rest = seq[:i] + seq[i+1:]
            for x in f(rest):
                yield seq[i:i+1] + x
a = [*f(['a', 'b'])]
b = [*f(['a', 'b', 'c', 'd'])]
print(a, len(b))

_ = [i for i in range(10)]
print(i)

def f(seq):
    for i in range(len(seq)):
        yield seq[i:] + seq[:i]
print((list(f('123'))))

{x + y: (x, y) for x in 'ab' for y in 'c' if not x.startswith('a')}

try:
    assert False, "assert"
    print("try")
except Exception as err:
    print(err)
else:
    print("else")

def f(*seqs, pad=None):
    maxlen = max(len(S) for S in seqs)
    index = range(maxlen)
    return [tuple((S[i] if len(S) > i else pad) for S in seqs) for i in index]
s1, s2 = 'ab' , 'xyz'
print(f(s1, s2))

def mymap(func, *seqs):
    res = []
    for args in zip( *seqs):
        res.append(func( *args))
    return res
x = [1, 2, 3]
y = [2, 3, 4, 5]
a = mymap(pow, x, y)
b = [*map(pow, x, y)]
print(a == b)

def f(seq):
    for i in range(len(seq)):
        seq = seq[1:] + seq[:1]
        yield seq
print(''.join(list(f('xy'))))

class MyExc(Exception): pass 
def f():
    raise MyExc()
    return  'f'
try:
    print(f())
    print('try')
except MyExc:
    print('exc')

x = 0
try:
    1/0
    x += 1
except ZeroDivisionError:
    x += 1
else: 
    x += 1
    1/0
    x += 1
print(x)