Một vài trick Python bạn nhất định phải biết trên con đường go-pro

>>> a, b, c = 1, 2, 3
>>> a, b, c
(1, 2, 3)
>>> a
1
>>> b
2
>>> c
3
>>> a, b, c = (2 * i + 1 for i in range(3))
>>> a, b, c
(1, 3, 5)
>>> a, (b, c), d = (1, (2, 3), 4)
>>> a, b, c, d
(1, 2, 3, 4)

>>> a, b = 1, 2
>>> a, b = b, a
>>> a, b
(2, 1)

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

>>> a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> a[-1]
10
>>> a[-3]
8

>>> a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> a[2:8]
[2, 3, 4, 5, 6, 7]

>>> a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> a[-4:-2]
[7, 8]

>>> a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> a[::2]
[0, 2, 4, 6, 8, 10]
>>> a[::3]
[0, 3, 6, 9]
>>> a[2:8:2]
[2, 4, 6]

>>> a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> a[::-1]
[10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
>>> a[::-2]
[10, 8, 6, 4, 2, 0]

>>> a = [1, 2, 3, 4, 5]
>>> a[2:3] = [0, 0]
>>> a
[1, 2, 0, 0, 4, 5]
>>> a[1:1] = [8, 9]
>>> a
[1, 8, 9, 2, 0, 0, 4, 5]
>>> a[1:-1] = []
>>> a
[1, 5]

>>> a = [0, 1, 2, 3, 4, 5]
>>> LASTTHREE = slice(-3, None)
>>> LASTTHREE
slice(-3, None, None)
>>> a[LASTTHREE]
[3, 4, 5]
a = [0, 1]
>>> a[LASTTHREE]
[0, 1]

>>> a = ['Hello', 'world', '!']
>>> for i, x in enumerate(a):
...     print('{}: {}'.format(i, x))
...
0: Hello
1: world
2: !

>>> m = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
>>> for k, v in m.items():
...     print('{}: {}'.format(k, v))
...
b: 2
c: 3
a: 1
d: 4

>>> a = [1, 2, 3]
>>> b = ['a', 'b', 'c']
>>> z = list(zip(a, b))
>>> z
[(1, 'a'), (2, 'b'), (3, 'c')]
>>> list(zip(*z))
[(1, 2, 3), ('a', 'b', 'c')]

>>> a = [1, 2, 3, 4, 5, 6]
>>> group_adjacent = lambda a, k: list(zip(*([iter(a)] * k)))
>>> group_adjacent(a, 3)
[(1, 2, 3), (4, 5, 6)]
>>> group_adjacent(a, 2)
[(1, 2), (3, 4), (5, 6)]
>>> group_adjacent(a, 1)
[(1,), (2,), (3,), (4,), (5,), (6,)]

>>> from itertools import islice
>>> a = [1, 2, 3, 4, 5, 6]
>>> group_adjacent = lambda a, k: list(zip(*(islice(a, i, None, k) for i in range(k))))
>>> group_adjacent(a, 3)
[(1, 2, 3), (4, 5, 6)]
>>> group_adjacent(a, 2)
[(1, 2), (3, 4), (5, 6)]
>>> group_adjacent(a, 1)
[(1,), (2,), (3,), (4,), (5,), (6,)]

>>> m = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
>>> m.items()
dict_items([('b', 2), ('c', 3), ('a', 1), ('d', 4)])
>>> list(zip(m.values(), m.keys()))
[(2, 'b'), (3, 'c'), (1, 'a'), (4, 'd')]
>>> mi = dict(zip(m.values(), m.keys()))
>>> mi
{1: 'a', 2: 'b', 3: 'c', 4: 'd'}

>>> import itertools
>>> a = [[1, 2], [3, 4], [5, 6]]
>>> list(itertools.chain.from_iterable(a))
[1, 2, 3, 4, 5, 6]

>>> a = [[1, 2], [3, 4], [5, 6]]
>>> sum(a, [])
[1, 2, 3, 4, 5, 6]

>>> a = [[1, 2], [3, 4], [5, 6]]
>>> [x for l in a for x in l]
[1, 2, 3, 4, 5, 6]
>>> a = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]
>>> [x for l1 in a for l2 in l1 for x in l2]
[1, 2, 3, 4, 5, 6, 7, 8]

>>> a = [1, 2, [3, 4], [[5, 6], [7, 8]]]
>>> latten = lambda x: [y for l in x for y in flatten(l)] if type(x) is list else [x]
>>> flatten(a)
[1, 2, 3, 4, 5, 6, 7, 8]

>>> g = (x ** 2 for x in range(10))
>>> next(g)
0
>>> next(g)
1
>>> next(g)
4
>>> sum(x ** 3 for x in range(10))
2025
>>> sum(x ** 3 for x in range(10) if x % 3 == 1)
408

>>> m = {x: x ** 2 for x in range(5)}
>>> m
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
>>> m = {x: 'A' + str(x) for x in range(10)}
>>> m
{0: 'A0', 1: 'A1', 2: 'A2', 3: 'A3', 4: 'A4', 5: 'A5', 6: 'A6', 7: 'A7', 8: 'A8', 9: 'A9'}

>>> m = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
>>> m
{'b': 2, 'c': 3, 'a': 1, 'd': 4}
>>> {v: k for k, v in m.items()}
{1: 'a', 2: 'b', 3: 'c', 4: 'd'}

>>> A = {1, 2, 3, 3}
>>> B = {3, 4, 5, 6, 7}
>>> A | B
{1, 2, 3, 4, 5, 6, 7}
>>> A & B
{3}
>>> A - B
{1, 2}
>>> B - A
{4, 5, 6, 7}
>>> A ^ B
{1, 2, 4, 5, 6, 7}
>>> A ^ B == ((A - B) | (B - A))
True

>>> import collections
>>> Point = collections.namedtuple('Point', ['x', 'y'])
>>> p = Point(x=1.0, y=2.0)
>>> p
Point(x=1.0, y=2.0)
>>> p.x
1.0
>>> p.y
2.0
>>> class Point(collections.namedtuple('PointBase', ['x', 'y'])):
...     __slots__ = ()
...     def __add__(self, other):
...         return Point(x=self.x + other.x, y=self.y + other.y)
...
>>> p = Point(x=1.0, y=2.0)
>>> q = Point(x=2.0, y=3.0)
>>> p + q
Point(x=3.0, y=5.0)

>>> import collections
>>> A = collections.Counter([1, 2, 2])
>>> B = collections.Counter([2, 2, 3])
>>> A
Counter({2: 2, 1: 1})
>>> B
Counter({2: 2, 3: 1})
>>> A | B
Counter({2: 2, 1: 1, 3: 1})
>>> A & B
Counter({2: 2})
>>> A + B
Counter({2: 4, 1: 1, 3: 1})
>>> A - B
Counter({1: 1})
>>> B - A
Counter({3: 1})

>>> import collections
>>> A = collections.Counter([1, 1, 2, 2, 3, 3, 3, 3, 4, 5, 6, 7])
>>> A
Counter({3: 4, 1: 2, 2: 2, 4: 1, 5: 1, 6: 1, 7: 1})
>>> A.most_common(1)
[(3, 4)]
>>> A.most_common(3)
[(3, 4), (1, 2), (2, 2)]

>>> import collections
>>> Q = collections.deque()
>>> Q.append(1)
>>> Q.appendleft(2)
>>> Q.extend([3, 4])
>>> Q.extendleft([5, 6])
>>> Q
deque([6, 5, 2, 1, 3, 4])
>>> Q.pop()
4
>>> Q.popleft()
6
>>> Q
deque([5, 2, 1, 3])
>>> Q.rotate(3)
>>> Q
deque([2, 1, 3, 5])
>>> Q.rotate(-3)
>>> Q
deque([5, 2, 1, 3])

>>> import collections
>>> last_three = collections.deque(maxlen=3)
>>> for i in range(10):
...     last_three.append(i)
...     print(', '.join(str(x) for x in last_three))
...
0
0, 1
0, 1, 2
1, 2, 3
2, 3, 4
3, 4, 5
4, 5, 6
5, 6, 7
6, 7, 8
7, 8, 9

>>> m = dict((str(x), x) for x in range(10))
>>> print(', '.join(m.keys()))
4, 6, 8, 2, 3, 7, 0, 9, 5, 1
>>> import collections
>>> m = collections.OrderedDict((str(x), x) for x in range(10))
>>> print(', '.join(m.keys()))
0, 1, 2, 3, 4, 5, 6, 7, 8, 9
>>> m = collections.OrderedDict((str(x), x) for x in range(10, 0, -1))
>>> print(', '.join(m.keys()))
10, 9, 8, 7, 6, 5, 4, 3, 2, 1

>>> m = dict()
>>> m['a']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'a'
>>> import collections
>>> m = collections.defaultdict(int)
>>> m['a']
0
>>> m['b']
0
>>> m = collections.defaultdict(str)
>>> m['a']
''
>>> m['b'] += 'a'
>>> m
defaultdict(<class 'str'>, {'b': 'a', 'a': ''})
>>> m = collections.defaultdict(lambda: '[default value]')
>>> m['a']
'[default value]'

>>> import collections
>>> import json
>>> tree = lambda: collections.defaultdict(tree)
>>> root = tree()
>>> root['menu']['id'] = 'file'
>>> root['menu']['value'] = 'File'
>>> root['menu']['menuitems']['new']['value'] = 'New'
>>> root['menu']['menuitems']['new']['onclick'] = 'new();'
>>> root['menu']['menuitems']['open']['value'] = 'Open'
>>> root['menu']['menuitems']['open']['onclick'] = 'open();'
>>> root['menu']['menuitems']['close']['value'] = 'Close'
>>> root['menu']['menuitems']['close']['onclick'] = 'close();'
>>> root
defaultdict(<function <lambda> at 0x7f5ce09e4488>, {'menu': defaultdict(<function <lambda> at 0x7f5ce09e4488>, {'value': 'File', 'menuitems': defaultdict(<function <lambda> at 0x7f5ce09e4488>, {'new': defaultdict(<function <lambda> at 0x7f5ce09e4488>, {'value': 'New', 'onclick': 'new();'}), 'close': defaultdict(<function <lambda> at 0x7f5ce09e4488>, {'value': 'Close', 'onclick': 'close();'}), 'open': defaultdict(<function <lambda> at 0x7f5ce09e4488>, {'value': 'Open', 'onclick': 'open();'})}), 'id': 'file'})})
>>> print(json.dumps(root, sort_keys=True, indent=4, separators=(',', ': ')))
{
    "menu": {
        "id": "file",
        "menuitems": {
            "close": {
                "onclick": "close();",
                "value": "Close"
            },
            "new": {
                "onclick": "new();",
                "value": "New"
            },
            "open": {
                "onclick": "open();",
                "value": "Open"
            }
        },
        "value": "File"
    }
}

>>> import collections
>>> import itertools
>>> value_to_numeric_map = collections.defaultdict(itertools.count().__next__)
>>> value_to_numeric_map['a']
0
>>> value_to_numeric_map['b']
1
>>> value_to_numeric_map['c']
2
>>> value_to_numeric_map['a']
0
>>> value_to_numeric_map['b']
1

>>> import heapq
>>> import random
>>> a = [random.randint(0, 100) for __ in range(100)]
>>> a
[77, 59, 53, 12, 57, 81, 90, 67, 62, 6, 93, 35, 28, 45, 32, 95, 55, 52, 0, 19, 99, 47, 3, 74, 15, 81, 69, 73, 94, 37, 51, 58, 36, 51, 57, 96, 15, 65, 4, 42, 42, 0, 36, 89, 34, 73, 12, 62, 13, 34, 84, 51, 92, 37, 17, 56, 59, 15, 8, 31, 36, 90, 70, 95, 41, 56, 100, 84, 50, 91, 72, 43, 15, 12, 90, 34, 58, 97, 72, 67, 79, 28, 84, 9, 25, 75, 47, 43, 100, 9, 27, 86, 12, 90, 4, 19, 45, 62, 91, 76]
>>> heapq.nsmallest(5, a)
[0, 0, 3, 4, 4]
>>> heapq.nlargest(5, a)
[100, 100, 99, 97, 96]

>>> import itertools
>>> for p in itertools.product('123', '45'):
...     print(''.join(p))
...
14
15
24
25
34
35
>>> for p in itertools.product('12', repeat=4):
...     print(''.join(p))
...
1111
1112
1121
1122
1211
1212
1221
1222
2111
2112
2121
2122
2211
2212
2221
2222

>>> import itertools
>>> for c in itertools.combinations('12345', 3):
...    print(''.join(c))
...
123
124
125
134
135
145
234
235
245
345
>>> for c in itertools.combinations_with_replacement('12345', 2):
...    print(''.join(c))
...
11
12
13
14
15
22
23
24
25
33
34
35
44
45
55

>>> import itertools
>>> for p in itertools.permutations('1234', 3):
...    print(''.join(p))
...
123
124
132
134
142
143
213
214
231
234
241
243
312
314
321
324
341
342
412
413
421
423
431
432

>>> import itertools
>>> a = [1, 2, 3, 4]
>>> for p in itertools.chain(itertools.combinations(a, 2), itertools.combinations(a, 3)):
...     print(p)
...
(1, 2)
(1, 3)
(1, 4)
(2, 3)
(2, 4)
(3, 4)
(1, 2, 3)
(1, 2, 4)
(1, 3, 4)
(2, 3, 4)
>>> for subset in itertools.chain.from_iterable(itertools.combinations(a, n) for n in range(len(a) + 1)):
...     print(subset)
...
()
(1,)
(2,)
(3,)
(4,)
(1, 2)
(1, 3)
(1, 4)
(2, 3)
(2, 4)
(3, 4)
(1, 2, 3)
(1, 2, 4)
(1, 3, 4)
(2, 3, 4)
(1, 2, 3, 4)

>>> import itertools
>>> for k, g in itertools.groupby('122333444455555'):
...     print(k, ''.join(g))
...
1 1
2 22
3 333
4 4444
5 55555
>>> m = {'a': 1, 'b': 2, 'c': 1, 'd': 2}
>>> sorted_m = dict(sorted(m.items(), key=lambda x: x[1]))
>>> for k, g in itertools.groupby(sorted_m, lambda x: x[1]):
...     print(k, ', '.join(e[0] for e in g))
...
1 c, a
2 b, d

>>> s = 'http://google.com'
>>> s.startswith('http://') or s.startswith('https://')
True
>>> s.startswith(('http://', 'https://'))
True

>>> s.endswith('.com') or s.endswith('.net')
True
>>> s.endswith(('.com', '.net'))
True
>>> isinstance(1, (int, float))
True

>>> 1 + 2
3
>>> _
3
>>> _ + 1
4
>>> foo = 'bar'
>>> foo
'bar'
>>> _ + 'foo'
'barfoo'

>>> def foo(l=[]):
...     l.append(1)
...     print(l)
...
>>> foo()
[1]
>>> foo()
[1, 1]
>>> foo()
[1, 1, 1]
>>> def foo(l=None):
...     l = l or []
...     l.append(1)
...     print(l)
...
>>> foo()
[1]
>>> foo()
[1]
>>> foo()
[1]

python3 -m http.server 8000
Serving HTTP on 0.0.0.0 port 8000 ...
127.0.0.1 - - [24/Jul/2017 13:56:51] "GET / HTTP/1.1" 200 -

>>> x = 2
>>> 3 > x == 1
False
>>> 1 < x < 3
True
>>> 10 < 10*x < 30
True
>>> 10 < x**5 < 30
False
>>> 100 < x*100 >= x**6 + 34 > x <= 2*x < 5
True

>>> list(reversed([1, 2, 3, 4]))
[4, 3, 2, 1]
>>> [1, 2, 3, 4][::-1]
[4, 3, 2, 1]
>>> tuple(reversed((1, 2, 3, 4)))
(4, 3, 2, 1)
>>> (1, 2, 3, 4)[::-1]
(4, 3, 2, 1)

>>> x = ['Hello', 'world', '!']
>>> ' '.join(x)
'Hello world !'

>>> class Foo:
...     def one(self):
...         return 1
...
>>> c = Foo()
>>> c.one()
1
>>> def two(self):
...     return 2
...
>>> Foo.two = two
>>> c.two()
2

>>> x = [1, 2, 3]
>>> dir(x)
['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

>>> x = [1, 2, 3]
>>> import sys
>>> sys.getsizeof(x)
88

>>> import pdb
>>> for i in range(10):
...     if i == 5:
...         pdb.set_trace()
...
> <stdin>(1)<module>()
(Pdb) i
5

>>> import this
The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!