pip install <package>
# python -m pip install <package>

import sys
print(sys.path)

import datetime

# 获取当前日期和时间
print(datetime.datetime.now())
# 2019-11-09 10:41:06.959435
print(type(now))
# <class 'datetime.datetime'>

# 获取指定日期和时间
dt = datetime.datetime(2017, 4, 19, 10, 30) # 用指定日期时间创建 datetime
print(dt)  # 2017-04-19 10:30:00

# datetime转换为timestamp
# 我们把1970年1月1日 00:00:00 UTC+00:00时区的时刻称为epoch time，
# 记为0（1970年以前的时间timestamp为负数），当前时间就是相对于
# epoch time的秒数，称为timestamp。
dt = datetime.datetime(2019, 10, 19, 10, 30, 25) # 用指定日期时间创建 datetime
print(str(dt.timestamp()))  # 1571452225.0

# 时间戳转 datetime
t = 1571452225.0
print(datetime.datetime.fromtimestamp(t))

# str转换为datetime
# 注意转换后的datetime是没有时区信息的
dt = datetime.datetime.strptime('2015-6-1 18:19:59', '%Y-%m-%d %H:%M:%S')

# datetime 转 str
datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')

import datetime

now = datetime.datetime.now()
now + datetime.timedelta(hours=10)
now - datetime.timedelta(days=2)

# 我们可以先通过utcnow()拿到当前的UTC时间，再转换为任意时区的时间

# 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)
2015-05-18 09:05:12.377316+00:00

# astimezone()将转换时区为北京时间:
>>> bj_dt = utc_dt.astimezone(timezone(timedelta(hours=8)))
>>> print(bj_dt)
2015-05-18 17:05:12.377316+08:00

# astimezone()将转换时区为东京时间:
>>> tokyo_dt = utc_dt.astimezone(timezone(timedelta(hours=9)))
>>> print(tokyo_dt)
2015-05-18 18:05:12.377316+09:00

# astimezone()将bj_dt转换时区为东京时间:
>>> tokyo_dt2 = bj_dt.astimezone(timezone(timedelta(hours=9)))
>>> print(tokyo_dt2)
2015-05-18 18:05:12.377316+09:00

import collections

Point = collections.namedtuple('Point', ['x', 'y'])
pt = Point(1, 2)
print(pt.x, pt.y)

# namedtuple 是 tuple 的子类
isinstance(pt, tuple)  # True

import collections

q = collections.deque(['a', 'b', 'c'])
q.append('x')
q.pop()
q.appendleft('x')
q.popleft()

import collections

d = collections.defaultdict(lambda: 'N/A')
print(d['new_key'])  # 'N/A'

import collections

d = OrderedDict()
od['z'] = 1
od['y'] = 2
od['x'] = 3
list(od.keys()) # 按照插入的Key的顺序返回
# ['z', 'y', 'x']

import collections

d1 = {'a': 1, 'b': 2}
d2 = {'a': 0, 'b': 3, 'c': 9}

cmap = collections.ChainMap(d1, d2)
print(cmap)
# ChainMap({'a': 1, 'b': 2}, {'a': 0, 'b': 3, 'c': 9})
print(cmap['a'])  # 1
print(cmap['c'])  # 9

import collections

counter = collections.Counter()
# Counter 实际上是 dict 的一个子类
isinstance(counter, dict)  # True

for ch in 'aabbbcccc':
    counter[ch] += 1
print(counter)
# Counter({'c': 4, 'b': 3, 'a': 2})

['A', 'B', 'C', ... 'a', 'b', 'c', ... '0', '1', ... '+', '/']

# b1        b2        b3
  1001 0001 0000 0100 1110 1011
# n1     n2      n3     n4

import base64

encoded = base64.b64encode(b'hello')
print(encoded)  # b'aGVsbG8='
print(type(encoded))  # <class 'bytes'>

decoded = base64.b64decode(encoded)
print(decoded)  # b'hello'
print(type(decoded))  # <class 'bytes'>
print(str(decoded, 'utf-8'))  # hello

import base64

base64.b64encode(b'i\xb7\x1d\xfb\xef\xff')
# b'abcd++//'
base64.urlsafe_b64encode(b'i\xb7\x1d\xfb\xef\xff')
# b'abcd--__'
base64.urlsafe_b64decode('abcd--__')
# b'i\xb7\x1d\xfb\xef\xff'

import struct

b = struct.pack('>I', 10240099)
# b'\x00\x9c@c'

x = struct.unpack('>I', b)
print(x)
# (10240099,)

import hashlib

md5 = hashlib.md5()
md5.update('hello world'.encode('utf-8'))
print(md5.hexdigest())
# 5eb63bbbe01eeed093cb22bb8f5acdc3

'e10adc3949ba59abbe56e057f20f883e': '123456'
'21218cca77804d2ba1922c33e0151105': '888888'
'5f4dcc3b5aa765d61d8327deb882cf99': 'password'

def calc_md5(password):
    return get_md5(password + 'the-Salt')

import hmac
message = b'Hello, world!'
key = b'secret'
h = hmac.new(key, message, digestmod='MD5')
# 如果消息很长，可以多次调用h.update(msg)
h.hexdigest()
# 'fa4ee7d173f2d97ee79022d1a7355bcf'

import itertools

# 无限的迭代
natuals = itertools.count(1)
for n in natuals:
    print(n)

# cycle()会把传入的一个序列无限重复下去：
cs = itertools.cycle('ABC')  # 注意字符串也是序列的一种
for c in cs:
    print(c)

# 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：
ns = itertools.repeat('A', 3)
for n in ns:
    print(n)

# 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：
natuals = itertools.count(1)
ns = itertools.takewhile(lambda x: x <= 10, natuals)
print(list(ns))
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

# chain()可以把一组迭代对象串联起来，形成一个更大的迭代器：
for c in itertools.chain('ABC', 'XYZ'):
    print(c)
# 迭代效果：'A' 'B' 'C' 'X' 'Y' 'Z'

# groupby()把迭代器中相邻的重复元素挑出来放在一起：
for key, group in itertools.groupby('AAABBBCCAAA'):
    print(key, list(group))
"""
A ['A', 'A', 'A']
B ['B', 'B', 'B']
C ['C', 'C']
A ['A', 'A', 'A']
"""

# groupby 支持传入一个求 key 值的函数，比如我们可以忽略大小写：
for key, group in itertools.groupby('AaaBBbcCAAa', lambda c: c.upper()):
    print(key, list(group))
"""
A ['A', 'a', 'a']
B ['B', 'B', 'b']
C ['c', 'C']
A ['A', 'A', 'a']
"""

try:
    f = open('/path/to/file', 'r')
    f.read()
finally:
    if f:
        f.close()

任何对象，只要正确实现了 **上下文管理** ，就可以用于 `with` 语句。

实现上下文管理是通过 `__enter__` 和 `__exit__` 这两个方法实现的。例如，下面的class实现了这两个方法：

```python
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)


# 把自己写的资源对象用于with语句：
with Query('Alice') as q:
    q.query()

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这个decorator接受一个generator，
# 用yield语句把with ... as var把变量输出出去，
# 然后，with语句就可以正常地工作了：
@contextmanager
def create_query(name):
    print('Begin')
    q = Query(name)
    yield q
    print('End')

with create_query('Bob') as q:
    q.query()

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

with tag("h1"):
    print("hello")
    print("world")
"""
<h1>
hello
world
</h1>
"""

from contextlib import closing
from urllib.request import urlopen

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

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

from urllib import request

with request.urlopen('https://api.douban.com/v2/book/2129650') 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'))

from urllib import request

req = request.Request('http://www.douban.com/')
# 添加HTTP头
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')
])

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')

# 传入 data 参数
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'))

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.build_opener(proxy_handler, proxy_auth_handler)
with opener.open('http://www.example.com/login.html') as f:
    pass

<a href="/">python</a>

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)

from html.parser import HTMLParser
from html.entities import name2codepoint

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&nbsp;tutorial...<br>END</p>
</body></html>''')

pip install pillow

from PIL import Image

# 打开一个jpg图像文件，注意是当前路径:
im = Image.open('test.jpg')

# 获得图像尺寸:
w, h = im.size
print('Original image size: %sx%s' % (w, h))

# 缩放到50%:
im.thumbnail((w//2, h//2))
print('Resize image to: %sx%s' % (w//2, h//2))

# 把缩放后的图像用jpeg格式保存:
im.save('thumbnail.jpg', 'jpeg')

# PIL 中提供了一些图像 filter
from PIL import ImageFilter

# 应用模糊滤镜:
im2 = im.filter(ImageFilter.BLUR)

from PIL import Image, ImageDraw, ImageFont, ImageFilter

import random

# 随机字母:
def rndChar():
    return chr(random.randint(65, 90))

# 随机颜色1:
def rndColor():
    return (random.randint(64, 255), random.randint(64, 255), random.randint(64, 255))

# 随机颜色2:
def rndColor2():
    return (random.randint(32, 127), random.randint(32, 127), random.randint(32, 127))

# 240 x 60:
width = 60 * 4
height = 60
image = Image.new('RGB', (width, height), (255, 255, 255))
# 创建Font对象:
font = ImageFont.truetype('Arial.ttf', 36)
# 创建Draw对象:
draw = ImageDraw.Draw(image)
# 填充每个像素:
for x in range(width):
    for y in range(height):
        draw.point((x, y), fill=rndColor())
# 输出文字:
for t in range(4):
    draw.text((60 * t + 10, 10), rndChar(), font=font, fill=rndColor2())
# 模糊:
image = image.filter(ImageFilter.BLUR)
image.save('code.jpg', 'jpeg')

pip install requests

import requests
r = requests.get('https://www.douban.com/') # 豆瓣首页
print(r.status_code)
# 200
print(r.text)
"""
'<!DOCTYPE HTML>\\n<html>\\n<head>\\n<meta name="description" content="提供图书、电影、音乐唱片的推荐、评论和...'
"""
print(r.encoding)
# 'utf-8'

import chardet

chardet.detect(b'Hello, world!')
# {'encoding': 'ascii', 'confidence': 1.0, 'language': ''}

import psutil

# 获取 CPU 信息
psutil.cpu_count() # CPU逻辑数量
psutil.cpu_count(logical=False) # CPU物理核心

# 统计CPU的用户／系统／空闲时间：
psutil.cpu_times()

# 实现类似top命令的CPU使用率，每秒刷新一次，累计10次：
for x in range(10):
    psutil.cpu_percent(interval=1, percpu=True)

# 获取内存信息
psutil.virtual_memory() # 物理内存
psutil.swap_memory()  # 交换内存

# 获取磁盘信息
psutil.disk_partitions() # 磁盘分区信息
psutil.disk_usage('/') # 磁盘使用情况
psutil.disk_io_counters() # 磁盘IO

# 获取网络信息
psutil.net_io_counters() # 获取网络读写字节／包的个数
psutil.net_if_stats() # 获取网络接口状态

# 获取进程信息
psutil.pids() # 所有进程ID
p = psutil.Process(3776) # 获取指定进程ID=3776

import psutil
psutil.test()