不怎么用到的Python技巧（1）

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获取Python的保留字

>>> import keyword
>>> print(keyword.kwlist)
['False', 'None', 'True', 'and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']

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判断是不是数字

>>> '十四'.isnumeric()
True
>>> '十四'.isdigit()
False
>>> '十四'.isdecimal()
False

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字符串对齐

>>> 'a'.rjust(5,'#')
'####a'
>>> 'a'.center(8,'#')
'###a####'
>>> 

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具名元组

>>> import collections
>>> Dog = collections.namedtuple('dogs', ['name', 'age', 'weight'])
>>> dog1 = Dog('Toto', 5, 20)
>>> dog1
dogs(name='Toto', age=5, weight=20)
>>> dog1._asdict()
OrderedDict([('name', 'Toto'), ('age', 5), ('weight', 20)])

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print()的参数

>>> print(1, 2, 3, sep = '-')
1-2-3
>>> print(1, 2, 3, end = '/')
1 2 3/

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局部变量

>>> a = 10    
>>> def test():
      "赋值则变成局部变量(这句通过__doc__可以查看)"
      a = a + 1
      print(a)
      
>>> test()    
Traceback (most recent call last):
  File "<pyshell#244>", line 1, in <module>
    test()
  File "<pyshell#243>", line 2, in test
    a = a + 1
UnboundLocalError: local variable 'a' referenced before assignment

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队列

不用直接用list做队列，其出列太耗资源。

>>> from collections import deque  
>>> q = deque([1, 2, 3])  
>>> q.append(4)  
>>> q 
deque([1, 2, 3, 4])
>>> q.popleft()
1
>>> q
deque([2, 3, 4])

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迭代器

实现__iter__即可

class MyCounter():
    def __iter__(self):
        self.a = 1
        return self

    def __next__(self):
        x = self.a
        self.a += 1
        return x

mycounter = MyCounter()
myiter = iter(mycounter)
print(next(myiter))

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漂亮打印pprint

没啥用

>>> from pprint import pprint
>>> pprint({"adf":123, "jj":8724}, indent=4, width=4)
{   'adf': 123,
    'jj': 8724}

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pickle与json

>>> import pickle, json
>>> data1 = {'abc': 1+2j}
>>> p = open('data.pkl', 'wb') # 必须是二进制bytes
>>> pickle.dump(data1, p)
>>> data2 = {'abc':123} #不能有复数
>>> f = open('data.json', 'w') # 必须是字符串str
>>> json.dump(data2, f)

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Python也有reduce

>>> from functools import reduce
>>> reduce(lambda x,y: x+y, [1,2,3])

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偏函数

固定了某函数的默认参数的函数

>>> from functools import partial
>>> max10 = partial(max, 10)
>>> max10(1,2)
10

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进程线程协程

这篇不错搞定python多线程和多进程

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base64编码

>>> b64 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
>>> ord('1')
49
>>> bin(49)
'0b110001'
>>> s = str(bin(49))
>>> s
'0b110001'
>>> s = s[2:].zfill(8).ljust(24, '0')
>>> s
'001100010000000000000000'
>>> s = [s[:6], s[7:12], s[13:18], s[19:]]      
>>> s       
['001100', '10000', '00000', '00000']
>>> b64[int(s[0], 2)]
'M'

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json序列化保留中文

>>> json.dumps({'asdf':'北京'}, ensure_ascii=False)
'{"asdf": "北京"}'

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