with context_expression [as target(s)]:
  with-body

try:
  f = open('/path/to/file', 'r', encoding='utf8', errors='ignore')
  print(f.read(1024))
finally:
  if f:
    f.close()
# 使用with语句
with open('/path/to/file', 'r') as f:
  print(f.read(1024))

import pickle
d = dict(name = 'sha', age = 26)
# 将序列化内容写入文件
with open('dump', 'wb') as f:
  pickle.dump(d, f)
# 从文件中读取序列化内容
with open('dump', 'rb') as f:
  d = pickle.load(f)
print(d) # {'name': 'sha', 'age': 26}

import os
pid = os.fork() # pid后的代码会在两个进程中分别执行，通过pid值不同判断父子
if pid == 0:
  print('exec in child process')
else:
  print('exec in parent process')
# exec in parent process
# exec in child process

from multiprocessing import Pool
def say(x):
  print(x)
if __name__ == '__main__':
  p = Pool(4)
  for i in range(5):
    p.apply_async(say, args=(i,))
  p.close()
  p.join()

import subprocess
print('$ nslookup amsimple.com')
r = subprocess.call(['nslookup', 'amsimple.com'])
print('Exit code:', r)

import threading
# 新线程执行的代码:
def say():
  print('%s say hello' % threading.current_thread().name)
t = threading.Thread(target=say, name = 'SayThread')
t.start()
t.join()

import threading
th_local = threading.local() # th_local会跟线程绑定，不同线程看到的是不同对象

import re
s = r'^[a-zA-Z0-9_-]+@[a-zA-Z0-9_-]+(\.[a-zA-Z0-9_-]+)+$'
re.match(s, 'shasharoman@gmail.com')