>>> import os.path
>>> os.path.join('/usr', 'local')
'/usr/local'
>>> os.path.dirname('/var/log')
'/var'

>>> from pathlib import Path
>>> Path('/usr') / Path('local')
PosixPath('/usr/local')
>>> Path('/usr') / 'local'
PosixPath('/usr/local')
>>> Path('/var/log').parent
PosixPath('/var')
>>> Path('/var/log').parent.name
'var'

class A: pass
a = A()
a.x = 1
a.__dict__
# {'x': 1}

a.__dict__[' '] = ' '
getattr(a, ' ')
# ' '

class Point:
    __slots__ = ['x', 'y']

class Parent: __slots__ = ['x']
class Child(Parent): __slots__ = ['y']
c = Child()
c.x = 1
c.y = 2

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

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'>)

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

class A:
    def __init__(self, x):
        self.x = x

    def __iadd__(self, another):
        self.x += another.x
        return self

    def __add__(self, another):
        return type(self)(self.x + another.x)

>>> a = [1, 2, 3]
>>> b = a
>>> a += [4]
>>> a
[1, 2, 3, 4]
>>> b
[1, 2, 3, 4]
>>> a = a + [5]
>>> a
[1, 2, 3, 4, 5]
>>> b
[1, 2, 3, 4]

>>> 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

try:
    1 / 0
except ZeroDivisionError:
    raise ValueError('Zero!')

(most recent call last):
  File "test.py", line 2, in <module>
    1 / 0
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "test.py", line 4, in <module>
    raise ValueError('Zero!')
ValueError: Zero!

division_error = None

try:
    1 / 0
except ZeroDivisionError as e:
    division_error = e

raise ValueError('Zero!') from division_error

(most recent call last):
  File "test.py", line 4, in <module>
    1 / 0
ZeroDivisionError: division by zero

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "test.py", line 8, in <module>
    raise ValueError('Zero!') from division_error
ValueError: Zero!

>>> 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]

package_broken = any(
    part.is_broken() for part in package.get_parts()
)
package_ok = all(
    part.ok() for part in package.get_parts()
)

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

{**{'a': 1}, 'b': 2, **{'c': 3}}
# Результат: {'a': 1, 'b': 2, 'c': 3}

[1, 2, *[3, 4]]
# Результат: [1, 2, 3, 4]

{**{'a': 1, 'b': 1}, 'a': 2, **{'b': 3}}
# Результат: {'a': 2, 'b': 3}

import asyncio

class Slow:
    def __init__(self, delay):
        self._delay = delay

    async def __aenter__(self):
        await asyncio.sleep(self._delay / 2)

    async def __aexit__(self, *exception):
        await asyncio.sleep(self._delay / 2)

async def main():
    async with Slow(1):
        print('slow')

loop = asyncio.get_event_loop()
loop.run_until_complete(main())

import asyncio
from contextlib import asynccontextmanager

@asynccontextmanager
async def slow(delay):
    half = delay / 2
    await asyncio.sleep(half)
    yield
    await asyncio.sleep(half)

async def main():
    async with slow(1):
        print('slow')

loop = asyncio.get_event_loop()
loop.run_until_complete(main())

>>> d = dict(a=1, b=2, c=3)
>>> assert d['a'] == 1
>>> assert d['c'] == 3

>>> assert d == dict(a=1, b=ANY, c=3)

>>> class AnyClass:
...     def __eq__(self, another):
...         return True
... 
>>> ANY = AnyClass()