python拾遗

发表于 2017-12-03 分类于 Python Disqus：

用来记录一些经常使用的 python 实现方法

优先队列

import heapq

class PriorityQueue(object):
    def __init__(self):
        self._queue = []
        self._index = 0
    
    def push(self, item, priority):
        heapq.heappush(self._queue, (-priority, self._index, item))
        self._index += 1
    
    def pop(self):
        return heapq.heappop(self._queue)[-1]
    
class Item(object):
    def __init__(self, name):
        self.name = name
    
    def __repr__(self):
        return 'Item(!r)'.format(self.name)

读取文件

CHUNK_SIZE = 1024

with open('test.json') as f:
    chunk = f.read(CHUNK_SIZE)
    while chunk:
        if chunk:
            print(chunk)
        chunk = f.read(CHUNK_SIZE)

from functools import partial

# Pythonic
with open('test.json') as f:
    for piece in iter(partial(f.read, CHUNK_SIZE), ''):
        print(piece)

# Lambda
with open('test.json') as f:
    for piece in iter(lambda: f.read(CHUNK_SIZE), ''):
        print(piece)

月度列表生成

知道历史上某个时间, 比如: 2008-08, 得到目前 2011-06 之间的年号和月份的列表

python列表以相同的数字为一组

例如 [0,0,0,1,1,2,2,2,3,0,4,4] –> [[0,0,0],[1,1],[2,2,2],[3],[0],[4,4]]

生成随机字符串

import random, string

# 方法 1
''.join(random.choice(string.ascii_letters + string.digits) for _ in range(15))

# 方法 2
s = ''
for _ in range(15):
    s += random.choice(string.ascii_letters + string.digits)
    
# 方法 3
''.join(random.choices(string.ascii_letters + string.digits, k=15))

写了一段代码来测试速度，生成一个100W长的随机字符串，最后发现速度: method 3>method 1>method 2。

Group by

生成并校验密码

from werkzeug.security import generate_password_hash, check_password_hash

class User(object):

    def __init__(self):
        self.password_hash = None

    @property
    def password(self):
        raise AttributeError("password is not a readable attribute.")

    @password.setter
    def password(self, password):
        self.password_hash = generate_password_hash(password)

    def verify_password(self, password):
        return check_password_hash(self.password_hash, password)

效果如下图所示

生成分数对应的成绩

def grade(score, breakpoints=[60, 70, 80, 90], grades='FDCBA'):
    i = bisect.bisect_left(breakpoints, score)
    return grades[i]

In [1]: [grade(score) for score in [33, 99, 77, 70, 89, 90, 100]]
Out[1]: ['F', 'A', 'C', 'D', 'B', 'B', 'A']

未完待续…

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