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

12345678910111213

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

123456789101112131415161718

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

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

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

3顺序字典

12345678

from collections import OrderedDictd = 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

from collections import Counterc = Counter()

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

5 itertools

从一开始生成自然数

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

在生成的可迭代序列中按规则筛选

1234	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

1234	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

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

123456789101112131415161718192021

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

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

123456789101112131415161718

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

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

@contextmanagerdef 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

12345678910111213141516171819202122232425262728293031323334353637383940

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: raisedef 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

from contextlib import closingfrom 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

@contextmanagerdef 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

123456789

@contextmanagerdef 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：

123456789

<h1>helloworld</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

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

123456789101112131415161718192021222324

from urllib import requestreq = 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, parseprint('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

123456789101112131415161718192021222324

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

12345678910111213

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

我的公众号：

转载于:https://www.cnblogs.com/secondtonone1/p/8067619.html