Python语句、函数与方法使用技巧 一波神奇的Python语句、函数与方法的使用技巧总结

#!/usr/bin/env python
# -*- coding: utf-8 -*-
from base import APIBase
from client import Client
from decorator import interface, export, stream
from server import Server
from storage import Storage
from util import (LogFormatter, disable_logging_to_stderr,
            enable_logging_to_kids, info)
__all__ = ['APIBase', 'Client', 'LogFormatter', 'Server',
      'Storage', 'disable_logging_to_stderr', 'enable_logging_to_kids',
      'export', 'info', 'interface', 'stream']

# 常见with使用场景
with open("test.txt", "r") as my_file: # 注意, 是__enter__()方法的返回值赋值给了my_file,
  for line in my_file:
    print line

#!/usr/bin/env python
# -*- coding: utf-8 -*-
class MyWith(object):
  def __init__(self):
    print "__init__ method"
  def __enter__(self):
    print "__enter__ method"
    return self # 返回对象给as后的变量
  def __exit__(self, exc_type, exc_value, exc_traceback):
    print "__exit__ method"
    if exc_traceback is None:
      print "Exited without Exception"
      return True
    else:
      print "Exited with Exception"
      return False
def test_with():
  with MyWith() as my_with:
    print "running my_with"
  print "------分割线-----"
  with MyWith() as my_with:
    print "running before Exception"
    raise Exception
    print "running after Exception"
if __name__ == '__main__':
  test_with()

__init__ method
__enter__ method
running my_with
__exit__ method
Exited without Exception
------分割线-----
__init__ method
__enter__ method
running before Exception
__exit__ method
Exited with Exception
Traceback (most recent call last):
 File "bin/python", line 34, in <module>
  exec(compile(__file__f.read(), __file__, "exec"))
 File "test_with.py", line 33, in <module>
  test_with()
 File "test_with.py", line 28, in test_with
  raise Exception
Exception

#!/usr/bin/env python
# -*- coding: utf-8 -*-
lst = [1, 2, 3, 4, 5, 6]
# 所有奇数都会返回True, 偶数会返回False被过滤掉
print filter(lambda x: x % 2 != 0, lst)
#输出结果
[1, 3, 5]

lst = [1, 2, 3]
new_lst = lst[0] if lst is not None else None
print new_lst
# 打印结果
1

# 单例装饰器
def singleton(cls):
  instances = dict() # 初始为空
  def _singleton(*args, **kwargs):
    if cls not in instances: #如果不存在, 则创建并放入字典
      instances[cls] = cls(*args, **kwargs)
    return instances[cls]
  return _singleton
@singleton
class Test(object):
  pass
if __name__ == '__main__':
  t1 = Test()
  t2 = Test()
  # 两者具有相同的地址
  print t1, t2

#!/usr/bin/env python

# -*- coding: utf-8 -*-
class A(object):
  # 普通成员函数
  def foo(self, x):
    print "executing foo(%s, %s)" % (self, x)
  @classmethod  # 使用classmethod进行装饰
  def class_foo(cls, x):
    print "executing class_foo(%s, %s)" % (cls, x)
  @staticmethod # 使用staticmethod进行装饰
  def static_foo(x):
    print "executing static_foo(%s)" % x
def test_three_method():
  obj = A()
  # 直接调用噗通的成员方法
  obj.foo("para") # 此处obj对象作为成员函数的隐式参数, 就是self
  obj.class_foo("para") # 此处类作为隐式参数被传入, 就是cls
  A.class_foo("para") #更直接的类方法调用
  obj.static_foo("para") # 静态方法并没有任何隐式参数, 但是要通过对象或者类进行调用
  A.static_foo("para")
if __name__ == '__main__':
  test_three_method()
  
# 函数输出
executing foo(<__main__.A object at 0x100ba4e10>, para)
executing class_foo(<class '__main__.A'>, para)
executing class_foo(<class '__main__.A'>, para)
executing static_foo(para)
executing static_foo(para)

#python内建函数
property(fget=None, fset=None, fdel=None, doc=None)

class Student(object):
  @property #相当于property.getter(score) 或者property(score)
  def score(self):
    return self._score
  @score.setter #相当于score = property.setter(score)
  def score(self, value):
    if not isinstance(value, int):
      raise ValueError('score must be an integer!')
    if value < 0 or value > 100:
      raise ValueError('score must between 0 ~ 100!')
    self._score = value

#!/usr/bin/env python
# -*- coding: utf-8 -*-
class TestIter(object):
  def __init__(self):
    self.lst = [1, 2, 3, 4, 5]
  def read(self):
    for ele in xrange(len(self.lst)):
      yield ele
  def __iter__(self):
    return self.read()
  def __str__(self):
    return ','.join(map(str, self.lst))
  
  __repr__ = __str__
def test_iter():
  obj = TestIter()
  for num in obj:
    print num
  print obj
if __name__ == '__main__':
  test_iter()

def partial(func, *part_args):
  def wrapper(*extra_args):
    args = list(part_args)
    args.extend(extra_args)
    return func(*args)
  return wrapper

#!/usr/bin/env python
# -*- coding: utf-8 -*-
from functools import partial
def sum(a, b):
  return a + b
def test_partial():
  fun = partial(sum, 2)  # 事先绑定一个参数, fun成为一个只需要一个参数的可调用变量
  print fun(3) # 实现执行的即是sum(2, 3)
if __name__ == '__main__':
  test_partial()
  
# 执行结果
5

#!/usr/bin/env python
# -*- coding: utf-8 -*-
def test_first():
  return 3
def test_second(num):
  return num
action = { # 可以看做是一个sandbox
    "para": 5,
    "test_first" : test_first,
    "test_second": test_second
    }
def test_eavl(): 
  condition = "para == 5 and test_second(test_first) > 5"
  res = eval(condition, action) # 解释condition并根据action对应的动作执行
  print res
if __name__ == '_

#!/usr/bin/env python
# -*- coding: utf-8 -*-
def test_first():
  print "hello"
def test_second():
  test_first()
  print "second"
def test_third():
  print "third"
action = {
    "test_second": test_second,
    "test_third": test_third
    }
def test_exec():
  exec "test_second" in action
if __name__ == '__main__':
  test_exec() # 无法看到执行结果

# 使用范例
class TestGetAttr(object):
  test = "test attribute"
  def say(self):
    print "test method"
def test_getattr():
  my_test = TestGetAttr()
  try:
    print getattr(my_test, "test")
  except AttributeError:
    print "Attribute Error!"
  try:
    getattr(my_test, "say")()
  except AttributeError: # 没有该属性, 且没有指定返回值的情况下
    print "Method Error!"
if __name__ == '__main__':
  test_getattr()
  
# 输出结果
test attribute
test method

def process_command_line(argv):
  """
  Return a 2-tuple: (settings object, args list).
  `argv` is a list of arguments, or `None` for ``sys.argv[1:]``.
  """
  if argv is None:
    argv = sys.argv[1:]
  # initialize the parser object:
  parser = optparse.OptionParser(
    formatter=optparse.TitledHelpFormatter(width=78),
    add_help_option=None)
  # define options here:
  parser.add_option(   # customized description; put --help last
    '-h', '--help', action='help',
    help='Show this help message and exit.')
  settings, args = parser.parse_args(argv)
  # check number of arguments, verify values, etc.:
  if args:
    parser.error('program takes no command-line arguments; '
           '"%s" ignored.' % (args,))
  # further process settings & args if necessary
  return settings, args
def main(argv=None):
  settings, args = process_command_line(argv)
  # application code here, like:
  # run(settings, args)
  return 0    # success
if __name__ == '__main__':
  status = main()
  sys.exit(status)

# 从csv中读取文件, 基本和传统文件读取类似
import csv
with open('data.csv', 'rb') as f:
  reader = csv.reader(f)
  for row in reader:
    print row
# 向csv文件写入
import csv
with open( 'data.csv', 'wb') as f:
  writer = csv.writer(f)
  writer.writerow(['name', 'address', 'age']) # 单行写入
  data = [
      ( 'xiaoming ','china','10'),
      ( 'Lily', 'USA', '12')]
  writer.writerows(data) # 多行写入

>>> name = "andrew"
>>> "my name is {name}".format(name=name)
'my name is andrew'