try:
    db_host = config['databases'][0]['hosts'][0]
except LookupError:
    db_host = 'localhost'

(x for x in range(100) if random() > 0.5)

class A:
    pass

class B(A):
    pass

class C(A):
    pass

class D(B, C):
    pass


print(D.__bases__)
# (<class '__main__.B'>, <class '__main__.C'>)

class B

print(D.__mro__)
# (<class '__main__.D'>, <class '__main__.B'>, <class '__main__.C'>, <class '__main__.A'>, <class 'object'>)

>>> def g():
...     print(1)
...     yield 1
...     print(2)
...     yield 2
...     print(3)
...     yield 3
...
>>> 2 in g()
1
2
True

In [1]: %timeit 10**20 in range(10**30)
375 ns ± 10.7 ns per loop

>>> first_odd = None
>>> for x in [2, 3, 4, 5]:
...     if x % 2 == 1:
...         first_odd = x
...         break
... else:
...     raise ValueError('В списке нет нечетных элементов')
...
>>> first_odd
3

>>> for x in [2, 4, 6]:
...     if x % 2 == 1:
...         first_odd = x
...         break
... else:
...     raise ValueError('В списке нет нечетных элементов')
...
...
ValueError: В списке нет нечетных элементов

with open('f') as f:
    with open('g') as g:
        with open('h') as h:
            pass

o = open
with o('f') as f, o('g') as g, o('h') as h:
    pass

with nested(o('f'), o('g'), o('h')) as (f, g, h):
    pass

with ExitStack() as stack:
    f = stack.enter_context(o('f'))
    g = stack.enter_context(o('g'))
    other = [
        stack.enter_context(o(filename))
        for filename in filenames
    ]

In [1]: class A:
   ...:     def __init__(self, x):
   ...:         self._x = x
   ...:
   ...:     def __repr__(self):
   ...:         class_name = type(self).__name__
   ...:         x = self._x
   ...:         return f'{class_name}({x!r})'
   ...:

In [2]: A(1)
Out[2]: A(1)

In [3]: A(2)
Out[3]: A(2)

In [4]: A(3)
Out[4]: A(3)

In [5]: [x for x in gc.get_objects() if isinstance(x, A)]
Out[5]: [A(1), A(2), A(3)]

int('୧৬𝟙༣')

1613

# Пример 1
int('෯')
# Вывод:
9

# Пример 2
'٢'.isdecimal()
# Вывод:
True

# Пример 3
import re
bool(re.match(r'\d', '౫'))
# Вывод:
True

>>> bool(datetime(2018, 1, 1).time())
False
>>> bool(datetime(2018, 1, 1, 13, 12, 11).time())
True

def create(created_time=None) -> None:
    if not created_time:
        created_time = datetime.now().time()

def create(created_time=None) -> None:
    if created_time is None:
        created_time = datetime.now().time()

async with aiofiles.open('filename', mode='r') as f:
    contents = await f.read()

>>> int("10")
10
>>> int("10", 2)
2
>>> def base2(x):
...     return int(x, 2)
...
>>> base2("10")
2

base2 = partial(int, base=2)

>>> map(partial(int, base=2), ["1", "10", "100"])
[1, 2, 4]

>>> map(lambda x: int(x, base=2), ["1", "10", "100"])
[1, 2, 4]

from contextlib import contextmanager

QUIT_MESSAGE = 'Bye'

def print_quit_mesage():
    global QUIT_MESSAGE
    print(QUIT_MESSAGE)

@contextmanager
def global_variable_changed(name, value):
    orig_value = globals()[name]
    globals()[name] = value
    yield
    globals()[name] = orig_value

with global_variable_changed(
    'QUIT_MESSAGE',
    'Tschüss'
):
    print_quit_mesage()

>>> dict(a=1, b=2)
{'a': 1, 'b': 2}
>>> {'a': 1, 'b': 2}
{'a': 1, 'b': 2}

>>> dict(a=1)
{'a': 1}
>>> dict(1='a')
  File "<stdin>", line 1
SyntaxError: keyword can't be an expression

>>> {'a': 1, 'a': 1}
{'a': 1}
>>> dict(a=1, a=1)
  File "<stdin>", line 1
SyntaxError: keyword argument repeated

>>> d = dict(b=2)
>>> dict(a=1, **d)
{'a': 1, 'b': 2}

>>> dict(b=3, **d)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: type object got multiple values for keyword argument