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  • 常用内建模块

    一.datetime

    1.模块导入:

    from datetime import datetime

    2.获取当前日期和时间:

    >>> now = datetime.now()
    >>> print(now)
    2019-01-13 14:19:38.181000
    

      

    3.获取指定日期和时间:

    >>> dt = datetime(2019,1,10,15,0)
    >>> print(dt)
    2019-01-10 15:00:00
    

      

    4.datetime转换为timestamp

    from datetime import datetime
    
    now = datetime.now()
    print(now.timestamp())
    

      

    注意:
    Python的timestamp是一个浮点数。如果有小数位,小数位表示毫秒数。

    5.timestamp转换为datetime

    #本地时区时间
    datetime.fromtimestamp(1547360695.313724)
    #UTC标准时区的时间
    print(datetime.utcfromtimestamp(1547360695.313724))
    

      

    6.str转换为datetime

    datetime.strptime('2015-6-1 18:19:59', '%Y-%m-%d %H:%M:%S')
    

      

    7.datetime转换为str

    now = datetime.now()
    print(now.strftime('%a, %b %d %H:%M'))
    

      

    8.datetime加减

    from datetime import datetime, timedelta
    now = datetime.now()
    new_time = now + timedelta(hours=10)
    print(new_time)
    

      

    9.本地时间转换为UTC时间

    from datetime import datetime, timedelta, timezone
    tz_utc_8 = timezone(timedelta(hours=8))
    now = datetime.now()
    dt = now.replace(tzinfo=tz_utc_8)
    print(dt)
    

      

    10.时区转换

    from datetime import datetime, timedelta, timezone
    
    # 强制设置时区为UTC+0:00:
    utc_dt = datetime.utcnow().replace(tzinfo=timezone.utc)
    print(utc_dt)
    #  利用astimezone()将转换时区为北京时间:
    bj_dt = utc_dt.astimezone(timezone(timedelta(hours=8)))
    print(bj_dt)
    

      

    注意:
    如果要存储datetime,最佳方法是将其转换为timestamp再存储,因为timestamp的值与时区完全无关

     二.collections


    1.namedtuple:给tuple属性命名

    from collections import namedtuple
    
    Point = namedtuple('Point', ['x', 'y', 'z'])
    p = Point(1,3,9)
    print(p.x, p.y, p.z)
    

      

    2.deque

    使用list存储数据时,按索引访问元素很快,但是插入和删除元素就很慢了,因为list是线性存储,数据量大的时候,插入和删除效率很低。
    deque是为了高效实现插入和删除操作的双向列表,适合用于队列和栈:

    from collections import deque
    q = deque([2,3,5])
    q.appendleft(6)
    q.popleft()
    print(q)
    

      

    3.defaultdict

    使用dict时,如果引用的Key不存在,就会抛出KeyError。如果希望key不存在时,返回一个默认值,就可以用defaultdict

    from collections import defaultdict
    
    d = defaultdict(lambda : 'N/A')
    d['l'] = 100
    print(d['l'])
    print(d['m'])
    

      

    4.OrderedDict

    使用dict时,Key是无序的。OrderedDict的Key会按照插入的顺序排列,可以实现FIFO

    from collections import OrderedDict
    
    d1 = OrderedDict()
    d1['a'] = 1
    d1['b'] = 2
    d1['c'] = 3
    print(d1)
    

      

    输出:
    OrderedDict([('a', 1), ('b', 2), ('c', 3)])

    5.ChainMap

    ChainMap可以把一组dict串起来并组成一个逻辑上的dict。ChainMap本身也是一个dict,但是查找的时候,会按照顺序在内部的dict依次查找

    from collections import ChainMap
    import os
    
    default_dict = {'platform': os.name}
    user_select = {'platform': 'posix'}
    
    d = ChainMap(user_select, default_dict)
    print(d['platform'])
    

      

    如果user_select存在platform就是用该值,否则就使用默认的

    6.Counter

    Counter是一个简单的计数器

    from collections import Counter
    
    c = Counter()
    for ch in 'helloworld':
        c[ch] += 1
    
    print(c)
    

      

    输出:
    Counter({'l': 3, 'o': 2, 'h': 1, 'e': 1, 'w': 1, 'r': 1, 'd': 1})

    三.base64

    Base64是一种用64个字符来表示任意二进制数据的方法,Base64编码会把3字节的二进制数据编码为4字节的文本数据,长度增加33%,好处是编码后的文本数据可以在邮件正文、网页等直接显示。

    如果要编码的二进制数据不是3的倍数,最后会剩下1个或2个字节怎么办?Base64用x00字节在末尾补足后,再在编码的末尾加上1个或2个=号,表示补了多少字节,解码的时候,会自动去掉。

    示例代码:

    import base64
    
    # base64编码
    base64_encode = base64.b64encode(b'52222')
    # base64安全编码,会将可能出现的字符字符+和/替换为-和_
    base64_safe_encode = base64.urlsafe_b64encode(b'52222')
    print(base64_encode)
    print(base64_safe_encode)
    
    # 解码
    print(base64.b64decode(base64_encode))
    print(base64.urlsafe_b64decode(base64_safe_encode))
    

      

    输出:
    b'NTIyMjI='
    b'NTIyMjI='
    b'52222'
    b'52222'

    四.struct

    Python提供了一个struct模块来解决bytes和其他二进制数据类型的转换

    import struct
    
    # 变成字节,>表示字节顺序是big-endian,也就是网络序,I表示4字节无符号整数
    print(struct.pack('>I', 10240099))
    # 字节变成相应的数据类型,根据>IH的说明,后面的bytes依次变为I:4字节无符号整数和H:2字节无符号整数。
    print(struct.unpack('>IH', b'xf0xf0xf0xf0x80x80'))
    

      

    五.hashlib

    md5/SHA1解密加密

    1.md5加密(32位长度)

    import hashlib
    
    #加密
    md5 = hashlib.md5()
    md5.update('hello'.encode('utf-8'))
    print(md5.hexdigest())
    

      

    2.SHA1(40位长度)

    import hashlib
    
    sha1 = hashlib.sha1()
    sha1.update('hello'.encode('utf-8'))
    print(sha1.hexdigest())
    

      

    六.hmac

    它通过一个标准算法,在计算哈希的过程中,把key混入计算过程中

    import hmac
    
    hmac_encode = hmac.new(b'salt', b'message', 'MD5')
    print(hmac_encode.hexdigest())
    

      

    七.itertools

    1.count:会创建一个无限的迭代器,是自然数序列:

    import itertools
    
    for i in itertools.count(1):
        print(i)
     
    

      

    2.cycle:会把传入的一个序列无限重复下去

    import itertools
    
    for i in itertools.cycle('abc'):
        print(i)
    

      

    3.repeat:负责把一个元素无限重复下去,不过如果提供第二个参数就可以限定重复次数

    4.无限序列虽然可以无限迭代下去,但是通常我们会通过takewhile()等函数根据条件判断来截取出一个有限的序列

    import itertools
    
    natuals = itertools.count(1)
    ns = itertools.takewhile(lambda x: x <= 10, natuals)
    print(list(ns))
    

      

    5.chain: 可以把一组迭代对象串联起来,形成一个更大的迭代器

    import itertools
    
    for i in itertools.chain('abc', 'def'):
        print(i)
    

      

    输出:
    a
    b
    c
    d
    e
    f

    6.groupby:把迭代器中相邻的重复元素挑出来放在一起

    import itertools
    
    for key, group in itertools.groupby('AAABBBCCAAA'):
        print(key, group)
    

      

    输出:
    A <itertools._grouper object at 0x000001C32D2A3550>
    B <itertools._grouper object at 0x000001C32D2DCDA0>
    C <itertools._grouper object at 0x000001C32D2A3550>
    A <itertools._grouper object at 0x000001C32D2DCD68>

    八.contextlib(with)

    任何对象,只要正确实现了上下文管理,就可以用于with语句.要使用with实现上下文管理是通过__enter__和__exit__这两个方法实现的

    1.通过类实现:

    class Query:
        def __enter__(self):
            print('enter')
            return self
    
        def query(self, params):
            print(params)
            return 100
    
        def __exit__(self, exc_type, exc_val, exc_tb):
            if exc_type:
                print('error')
            else:
                print('exit')
    
    with Query() as query:
        query.query('rorshach')
    

      

    2.更加简便的通过@contextmanager和yield实现:

    from contextlib import contextmanager
    
    class Query:
        def query(self, params):
            print(params)
            return 100
    
    @contextmanager
    def make_context_query():
        q = Query()
        yield q
    
    with make_context_query() as query:
        query.query('rorshach')
    

      

    很多时候,我们希望在某段代码执行前后自动执行特定代码,也可以用@contextmanager实现:

    from contextlib import contextmanager
    
    @contextmanager
    def tag():
        print('<h1>')
        yield
        print('</h1>')
    
    #yield没有生成值,with语句中就不需要写as子句了
    with tag() as tag:
        print('hello')
    

      

    输出:
    <h1>
    hello
    </h1>

    如果出错,关闭对象示例:

    from contextlib import contextmanager
    from urllib.request import urlopen
    
    @contextmanager
    def closing(thing):
        try:
            yield thing
        finally:
            thing.close()
    
    with closing(urlopen('http://www.baidu.com')) as page:
        for line in page:
            print(line)
    

      

    九.urllib

    1.get请求

    from urllib import request
    
    req = request.Request('http://www.baidu.com/')
    # 设置ua
    req.add_header('User-Agent', 'Mozilla/6.0 (iPhone; CPU iPhone OS 8_0 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/8.0 Mobile/10A5376e Safari/8536.25')
    with request.urlopen(req) as f:
        print('Status:', f.status, f.reason)
        for k, v in f.getheaders():
            print('%s: %s' % (k, v))
        print('Data:', f.read().decode('utf-8'))
    

      

    2.post请求

    from urllib import request, parse
    
    print('Login to weibo.cn...')
    email = input('Email: ')
    passwd = input('Password: ')
    login_data = parse.urlencode([
        ('username', email),
        ('password', passwd),
        ('entry', 'mweibo'),
        ('client_id', ''),
        ('savestate', '1'),
        ('ec', ''),
        ('pagerefer', 'https://passport.weibo.cn/signin/welcome?entry=mweibo&r=http%3A%2F%2Fm.weibo.cn%2F')
    ])
    
    req = request.Request('https://passport.weibo.cn/sso/login')
    req.add_header('Origin', 'https://passport.weibo.cn')
    req.add_header('User-Agent', 'Mozilla/6.0 (iPhone; CPU iPhone OS 8_0 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/8.0 Mobile/10A5376e Safari/8536.25')
    req.add_header('Referer', 'https://passport.weibo.cn/signin/login?entry=mweibo&res=wel&wm=3349&r=http%3A%2F%2Fm.weibo.cn%2F')
    
    with request.urlopen(req, data=login_data.encode('utf-8')) as f:
        print('Status:', f.status, f.reason)
        for k, v in f.getheaders():
            print('%s: %s' % (k, v))
        print('Data:', f.read().decode('utf-8'))
    

      

    十.XML

    1.DOM:

    DOM会把整个XML读入内存,解析为树,因此占用内存大,解析慢,优点是可以任意遍历树的节点

    示例代码:

    from xml.parsers.expat import ParserCreate
    
    class DefaultSaxHandler(object):
        def start_element(self, name, attrs):
            print('sax:start_element: %s, attrs: %s' % (name, str(attrs)))
    
        def end_element(self, name):
            print('sax:end_element: %s' % name)
    
        def char_data(self, text):
            print('sax:char_data: %s' % text)
    
    xml = r'''<?xml version="1.0"?>
    <ol>
        <li><a href="/python">Python</a></li>
        <li><a href="/ruby">Ruby</a></li>
    </ol>
    '''
    
    handler = DefaultSaxHandler()
    parser = ParserCreate()
    parser.StartElementHandler = handler.start_element
    parser.EndElementHandler = handler.end_element
    parser.CharacterDataHandler = handler.char_data
    parser.Parse(xml)
    

      

    2.SAX是流模式,边读边解析,占用内存小,解析快,缺点是我们需要自己处理事件

    十一.HTMLParser

    from html.parser import HTMLParser
    
    class MyHTMLParser(HTMLParser):
    
        def handle_starttag(self, tag, attrs):
            print('<%s>' % tag)
    
        def handle_endtag(self, tag):
            print('</%s>' % tag)
    
        def handle_startendtag(self, tag, attrs):
            print('<%s/>' % tag)
    
        def handle_data(self, data):
            print(data)
    
        def handle_comment(self, data):
            print('<!--', data, '-->')
    
        def handle_entityref(self, name):
            print('&%s;' % name)
    
        def handle_charref(self, name):
            print('&#%s;' % name)
    
    parser = MyHTMLParser()
    parser.feed('''<html>
    <head></head>
    <body>
    <!-- test html parser -->
        <p>Some <a href="#">html</a> HTML tutorial...<br>END</p>
    </body></html>''')
    

      

      

     

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  • 原文地址:https://www.cnblogs.com/itfenqing/p/10275132.html
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