值得收藏，Python 开发中的高级技巧

> chars = [ c for c in 'python' ]
> chars
['p', 'y', 't', 'h', 'o', 'n']

> dict1 = {'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5}
> double_dict1 = {k:v*2 for (k,v) in dict1.items()}
> double_dict1
{'a': 2, 'b': 4, 'c': 6, 'd': 8, 'e': 10}

> set1 = {1,2,3,4}
> double_set = {i*2 for i in set1}
> double_set
{8, 2, 4, 6}

> x = {'a':1,'b':2}
> y = {'c':3, 'd':4}
> z = {**x, **y}
> z
{'a': 1, 'b': 2, 'c': 3, 'd': 4}

> nums = [1,2,3]
> nums[::]
[1, 2, 3]
> copy_nums = nums[::]
> copy_nums
[1, 2, 3]

> reverse_nums = nums[::-1]
> reverse_nums
[3, 2, 1]
 PACKING / UNPACKING

> a,b = 1, 2
> a ,b = b,a
> a
2
> b
1

> a, *b = 1,2,3
> a
1
> b
[2, 3]

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

> def f():
...   return 1, 2, 3, 4
...
> a, b, c, d = f()
> a
1
> d
4

> " ".join(["I", "Love", "Python"])
'I Love Python'

> if a > 2 and a < 5:
...   pass
...
> if 2<a<5:
...   pass
yield from
# 没有使用 field from
def dup(n):
  for i in range(n):
    yield i
    yield i
# 使用yield from
def dup(n):
  for i in range(n):
  yield from [i, i]
for i in dup(3):
  print(i)
>
0
0
1
1
2
2

> if x == 1 or x == 2 or x == 3:
...   pass
...
> if x in (1,2,3):
...   pass

def fun(x):
  if x == 'a':
    return 1
  elif x == 'b':
    return 2
  else:
    return None
def fun(x):
  return {"a": 1, "b": 2}.get(x)

> for i, e in enumerate(["a","b","c"]):
...   print(i, e)
...
0 a
1 b
2 c

> g = (i**2 for i in range(5))
> g
<generator object <genexpr> at 0x10881e518>
> for i in g:
...   print(i)
...
0
1
4
9
16

> d = dict()
> d['nums']
KeyError: 'nums'
>
> from collections import defaultdict
> d = defaultdict(list)
> d["nums"]
[]

> lang = 'python'
> f'{lang} is most popular language in the world'
'python is most popular language in the world'

> nums = [1,2,3,3]
> max(set(nums), key=nums.count)
3

from collections import Counter
> Counter(nums).most_common()[0][0]
3

> with open("test.txt", "w") as f:
...   f.writelines("hello")

> isinstance(a, (int, str))
True

> "http://foofish.net".startswith(('http','https'))
True
> "https://foofish.net".startswith(('http','https'))
True
__str__ 与 __repr__ 区别
> str(datetime.now())
'2018-11-20 00:31:54.839605'
> repr(datetime.now())
'datetime.datetime(2018, 11, 20, 0, 32, 0, 579521)'

def makebold(f):
return lambda: "<b>" + f() + "</b>"
def makeitalic(f):
return lambda: "<i>" + f() + "</i>"
@makebold
@makeitalic
def say():
return "Hello"
> say()
<b><i>Hello</i></b>

def say():
return "Hello"
> makebold(makeitalic(say))()
<b><i>Hello</i></b>