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  • python学习(十五) 内建模块学习

    介绍python的几个內建模块，原文链接

    1 python的时间模块datetime

    取现在时间

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

    　　


    将指定日期转化为时间戳     

    from datetime import datetime
dt = datetime(2017,12,13,13,7)
# 把datetime转换为timestamp
print( dt.timestamp() )

    　　

    将时间戳转化为日期

    from datetime import datetime
t = 1429417200.0
print(datetime.fromtimestamp(t))

    　　

    根据时间戳转化为本地时间和utc时间

    from datetime import datetime
t = 1429417200.0
# 本地时间
print(datetime.fromtimestamp(t))
# UTC时间 
print(datetime.utcfromtimestamp(t))

    　　


    将字符串转化为时间     

    from datetime import datetime
cday = datetime.strptime('2017-6-1 18:22:22','%Y-%m-%d %H:%M:%S')
print(day)

    　　

    将时间戳转化为字符串

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

    　　

    时间加减

    from datetime import datetime , timedelta
now = datetime.now()
print( now )
print(now + timedelta(hours = 10))
print(now + timedelta(days = 1))
print(now + timedelta(days = 2, hours = 12))

    　　

    设置时区 

    from datetime import datetime, timedelta, timezone
# 创建时区UTC+8:00
timezone_8 = timezone(timedelta(hours = 8) )
now = datetime.now()
print(now)
# 强制设置为UTC+8:00
dt = now.replace(tzinfo=timezone_8)
print(dt)

    　　

    获取utc时区和时间，并且转化为别的时区的时间

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    from datetime import datetime, timedelta, timezone

    # 拿到UTC时间，并强制设置时区为UTC+0:00:
    utc_dt = datetime.utcnow().replace(tzinfo=timezone.utc)
    print(utc_dt)
    bj_dt = utc_dt.astimezone(timezone(timedelta(hours = 8) ))
    print(bj_dt)

    tokyo_dt = utc_dt.astimezone(timezone(timedelta(hours = 9) ) )
    print(tokyo_dt)

    tokyo_dt2 = bj_dt.astimezone(timezone(timedelta(hours = 9) ) )
    print(tokyo_dt2)

    2命名tuple

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    #可命名tuple
    from collections import namedtuple
    Point = namedtuple('Point', ['x','y'])
    p = Point(1,2)
    print(p.x)

    from collections import deque
    q = deque(['a','b','c'])
    q.append('x')
    q.appendleft('y')
    print(q)


    from collections import defaultdict
    dd = defaultdict(lambda:'N/A')
    dd['key1']='abc'
    print(dd['key1'])
    print(dd['key2'])

    3顺序字典

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    from collections import OrderedDict
    d = dict([ ['a',1], ['b',2],['c',3]])
    print(d)
    od = OrderedDict([('a',1),('b',2),('c',3)])
    print(od)

    od2 = OrderedDict([['Bob',90],['Jim',20],['Seve',22]])
    print(od2)

    4计数器

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    from collections import Counter
    c = Counter()

    for ch in 'programming':
    	c[ch]=c[ch]+1

    5 itertools

    从一开始生成自然数

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    #itertools.count(start , step)
    import itertools
    natuals = itertools.count(1)
    for n in natuals:
    	print(n)

    在生成的可迭代序列中按规则筛选

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

    将两个字符串生成一个序列

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    for c in itertools.chain('ABC','XYZ'):
    	print(c)

    print(list(itertools.chain('ABC','XYZ')) )

    迭代器把连续的字母放在一起分组

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

    for key, group in itertools.groupby('AaaBBbcCAAa', lambda c: c.upper() ):
    	print(key,list(group))

    6 contextmanager

    open 返回的对象才可用with，或者在类中实现enter和exit可以使该类对象支持with用法

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    class Query(object):
    	def __init__(self, name):
    		self.name = name
    	
    	def __enter__(self):
    		print('Begin')
    		return self

    	def __exit__(self, exc_type, exc_value, traceback):
    		if exc_type:
    			print('Error')
    		else:
    			print('End')

    	def query(self):
    		print('Query info about %s...' %self.name)		


    with Query('BBBB') as q:
    	if q:
    		q.query()

    简单介绍下原理

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    with EXPR as VAR:
    实现原理:
    在with语句中, EXPR必须是一个包含__enter__()和__exit__()方法的对象(Context Manager)。
    调用EXPR的__enter__()方法申请资源并将结果赋值给VAR变量。
    通过try/except确保代码块BLOCK正确调用，否则调用EXPR的__exit__()方法退出并释放资源。
    在代码块BLOCK正确执行后，最终执行EXPR的__exit__()方法释放资源。

    通过python提供的装饰器contextmanager，作用在生成器函数，可以达到with操作的目的

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    from contextlib import contextmanager
    class Query(object):
    	def __init__(self, name):
    		self.name = name

    	def query(self):
    		print('Query info about %s ...' %self.name)

    @contextmanager
    def create_query(name):
    	print('Begin')
    	q = Query(name)
    	yield q
    	print('End')

    with create_query('aaa') as q:
    	if q:
    		print(q.query())

    可以看看contextmanager源码，了解下

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    class GeneratorContextManager(object):
    	def __init__(self, gen):
            self.gen = gen

        def __enter__(self):
            try:
                return self.gen.next()
            except StopIteration:
                raise RuntimeError("generator didn't yield")
    ​
        def __exit__(self, type, value, traceback):
            if type is None:
                try:
                    self.gen.next()
                except StopIteration:
                    return
                else:
                    raise RuntimeError("generator didn't stop")
            else:
                try:
                    self.gen.throw(type, value, traceback)
                    raise RuntimeError("generator didn't stop after throw()")
                except StopIteration:
                    return True
                except:
                    # only re-raise if it's *not* the exception that was
                    # passed to throw(), because __exit__() must not raise
                    # an exception unless __exit__() itself failed.  But
                    # throw() has to raise the exception to signal
                    # propagation, so this fixes the impedance mismatch 
                    # between the throw() protocol and the __exit__()
                    # protocol.
                    #
                    if sys.exc_info()[1] is not value:
                        raise
    ​
    def contextmanager(func):
        def helper(*args, **kwds):
            return GeneratorContextManager(func(*args, **kwds))
        return helper

    也可以采用closing用法作用在一个对象上支持with open操作

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    from contextlib import closing
    from urllib.request import urlopen

    with closing(urlopen('https://www.python.org')) as page:
        for line in page:
            print(line)

    介绍下closing 实现原理

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    @contextmanager
    def closing(thing):
        try:
            yield thing
        finally:
            thing.close()

    同样可以用contextmanager实现打印指定标签的上下文对象

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    @contextmanager
    def tag(name):
        print("<%s>" % name)
        yield
        print("</%s>" % name)

    with tag("h1"):
        print("hello")
        print("world")

    上述代码执行结果为：

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    <h1>
    hello
    world
    </h1>
    代码的执行顺序是：

    with语句首先执行yield之前的语句，因此打印出<h1>；
    yield调用会执行with语句内部的所有语句，因此打印出hello和world；
    最后执行yield之后的语句，打印出</h1>。

    7 urllib库

    这是个非常重要的库，做爬虫会用到

    采用urllib get网页信息

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    from urllib import request 
    with request.urlopen('http://www.limerence2017.com/') as f:
    	data = f.read()
    	print('Status:', f.status, f.reason)
    	for k, v in f.getheaders():
    		print('%s: %s' %(k,v))
    	print('Data:', data.decode('utf-8') )

    在request中添加信息头模拟浏览器发送请求

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    from urllib import request
    req = request.Request('http://www.douban.com/')
    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'))


    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')
    ])

    采用post方式获取信息, request.urlopen()，参数可以携带data发送给网址

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    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'))

    采用代理方式获取网页信息

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    proxy_handler = urllib.request.ProxyHandler({'http': 'http://www.example.com:3128/'})
    proxy_auth_handler = urllib.request.ProxyBasicAuthHandler()
    proxy_auth_handler.add_password('realm', 'host', 'username', 'password')
    opener = urllib.request.bulid_opener(proxy_handler, proxy_auth_handler)
    with opener.open('http://www.example.com/login.html') as f:
    	pass


    proxy_auth_handler = urllib.request.ProxyBasicAuthHandler()
    proxy_auth_handler.add_password('realm', 'host', 'username', 'password')
    opener = urllib.request.build_opener(proxy_handler, proxy_auth_handler)
    with opener.open('http://www.example.com/login.html') as f:
        pass

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  • 原文地址：https://www.cnblogs.com/secondtonone1/p/8067619.html
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