Andrey Dugin

pd.get_dummies(df[['event', 'city']], prefix='', prefix_sep='', columns=['event']).groupby('city').sum()

from itertools import chain

N = 7
for n in chain(range(1, N + 1, 2), range(N - 2, 0, -2)):
    print(f'{{:^{N}}}'.format('*' * n))
    # print('{{:^{}}}'.format(N).format('*' * n))

>>> '{:<30}'.format('left aligned')
'left aligned                  '
>>> '{:>30}'.format('right aligned')
'                 right aligned'
>>> '{:^30}'.format('centered')
'           centered           '
>>> '{:*^30}'.format('centered')  # use '*' as a fill char
'***********centered***********'

from functools import reduce
from operator import mul

def persistence(n):
    i = 0
    while n > 9:
        n = reduce(mul, map(int, str(n)), 1)
        i += 1
    return i

def persistence(n):
    i = 0
    while n > 9:
        n = eval('*'.join(f'{n}'))
        i += 1
    return i

from functools import reduce
from operator import mul
from itertools import count

def persistence(n):
    for i in count(0):
        if n > 9:
            n = reduce(mul, map(int, str(n)), 1)
        else:
            return i

assert persistence(39) == 3
assert persistence(999) == 4
assert persistence(4) == 0

def square_digits_v1(n):
    return int(''.join(str(int(x) ** 2) for x in str(n)))

def square_digits_v2(n, t=str.maketrans({str(d): str(d ** 2) for d in range(10)})):
    return int(str(n).translate(t))

def square_digits_v3(n):  # import re
    return int(re.sub('\d', lambda m: str(int(m.group(0)) ** 2), str(n)))

def square_digits_v4(n):  # import numpy as np
    return int(''.join((np.fromiter(str(n), int) ** 2).astype(str)))

def square_digits_v5(n):  # Только вывод на печать
    print(*[int(x) ** 2 for x in str(n)], sep='')

from decimal import Decimal
from io import StringIO

def square_digits_v6(n):
    with StringIO() as buffer:
        for digit in Decimal(n).as_tuple().digits:
            print(digit ** 2, end='', file=buffer)
        return int(buffer.getvalue())

as_int = lambda f: lambda x: int(f(x))

@as_int
def square_digits_v7(n):
    return eval('f"{'+'**2}{'.join(f'{n}')+'**2}"')

import re

def flatten(lst):
    return [int(x) for x in re.findall('\d+', str(lst))]

from itertools import chain

def flatten(seq):
    try:
        yield from chain.from_iterable(flatten(x) for x in seq if x is not None)
    except TypeError:
        yield seq

flat_list = list(flatten(lst))

def flatten(seq):
    try:
        yield from chain(*map(flatten, seq))
    except TypeError:
        yield seq