python tips

1、enum

#!/usr/bin/env python
# -*- coding:utf-8 -*-

def enum(**enums):
    return type('Enum', (), enums)
Gender = enum(MALE=0,FEMALE=1)
print Gender.MALE
print Gender.FEMALE

2、检查字符串是否是number

s='123456789'
s.isdigit()#return True

3、list取交集

s=[1,2,3]
w=[2,3,4]
list(set(s).intersection(w))

4、两个list转成一个dict

dict(zip(a,b))

5、singleton

def singleton(cls):
    instances = {}
    def get_instance():
        if cls not in instances:
            instances[cls] = cls()
        return instances[cls]
    return get_instance

第二种tornado IOLoop中使用的单例模式：

    @staticmethod
    def instance():
        """Returns a global IOLoop instance.

        Most single-threaded applications have a single, global IOLoop.
        Use this method instead of passing around IOLoop instances
        throughout your code.

        A common pattern for classes that depend on IOLoops is to use
        a default argument to enable programs with multiple IOLoops
        but not require the argument for simpler applications::

            class MyClass(object):
                def __init__(self, io_loop=None):
                    self.io_loop = io_loop or IOLoop.instance()
        """
        if not hasattr(IOLoop, "_instance"):
            with IOLoop._instance_lock:
                if not hasattr(IOLoop, "_instance"):
                    # New instance after double check
                    IOLoop._instance = IOLoop()
        return IOLoop._instance

6、list排重

{}.fromkeys(list).keys()

未完待续...

参考资料：
http://stackoverflow.com/questions/36932/whats-the-best-way-to-implement-an-enum-in-python
http://stackoverflow.com/questions/354038/how-do-i-check-if-a-string-is-a-number-in-python
http://docs.python.org/2/library/stdtypes.html#str.isdigit