字符串格式化

>>> "{key}={value}".format(key="a", value=10) # 使⽤命名参数'a=10'>>> "[{0:<10}], [{0:^10}], [{0:*>10}]".format("a") # 左中右对⻬'[a         ], [    a     ], [*********a]'>>> "{0.platform}".format(sys) # 成员'darwin'>>> "{0[a]}".format(dict(a=10, b=20)) # 字典'10'>>> "{0[5]}".format(range(10)) # 列表'5'>>> "My name is {0} :-{
   {}}".format('Fred') # 真得想显示{},需要双{}'My name is Fred :-{}'>>> "{0!r:20}".format("Hello")"'Hello'             ">>> "{0!s:20}".format("Hello")'Hello               '>>> "Today is: {0:%a %b %d %H:%M:%S %Y}".format(datetime.now())'Today is: Mon Mar 31 23:59:34 2014'

列表去重

>>> l = [1, 2, 2, 3, 3, 3]>>> {}.fromkeys(l).keys()[1, 2, 3] # 列表去重(1)>>> list(set(l)) # 列表去重(2)[1, 2, 3]In [2]: %timeit list(set(l))1000000 loops, best of 3: 956 ns per loopIn [3]: %timeit {}.fromkeys(l).keys()1000000 loops, best of 3: 1.1 µs per loopIn [4]: l = [random.randint(1, 50) for i in range(10000)]In [5]: %timeit list(set(l))1000 loops, best of 3: 271 µs per loopIn [6]: %timeit {}.fromkeys(l).keys()1000 loops, best of 3: 310 µs per loop PS: 在字典较大的情况下, 列表去重(1)略慢了

super 当子类调用父类属性时一般的做法是这样

>>> class LoggingDict(dict): ...     def __setitem__(self, key, value):...         print('Setting {0} to {1}'.format(key, value))...         dict.__setitem__(self, key, value)

问题是假如你继承的不是dict而是其他,那么就要修改2处,其实可以这样

>>> class LoggingDict(dict):...     def __setitem__(self, key, value):...         print('Setting {0} to {1}'.format(key, value))...         super(LoggingDict, self).__setitem__(key, value)

PS: 感觉super自动找到了LoggingDict的父类(dict)，然后把self转化为其实例

斐波那契数列

>>> import itertools>>>>>> def fib():...     a, b = 0, 1...     while 1:...         yield b...         a, b = b, a + b...>>>>>> print list(itertools.islice(fib(), 10))[1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

看到这里, 就得说说contextmanager

@contextlib.contextmanagerdef some_generator(
    
     ):    
     
          try:        yield 
      
           finally:        
       
        with some_generator(
        
         ) as 
         
          : 
         
        
       
      
     
    

也就是:

    
         try:        
     
       = 
                  finally:        
       
      
     
    

contextmanager例子(一)

>>> lock = threading.Lock()>>> @contextmanager... def openlock():...     print('Acquire')...     lock.acquire()...     yield...     print('Releasing')...     lock.release()... >>> with openlock():...     print('Lock is locked: {}'.format(lock.locked()))...     print 'Do some stuff'... AcquireLock is locked: TrueDo some stuffReleasing

__slots__ 大量属性时减少内存占用

>>> class User(object):...     __slots__ = ("name", "age")...     def __init__(self, name, age):...         self.name = name...         self.age = age...>>> u = User("Dong", 28)>>> hasattr(u, "__dict__")False>>> u.title = "xxx"Traceback (most recent call last):  File "
    
     ", line 1, in 
     
      AttributeError: 'User' object has no attribute 'title'
     
    

模块: itertools(一)

>>> def chunker(items, chunk_size):...     for _key, group in itertools.groupby(...         enumerate(items), lambda x: x[0] // chunk_size):...             yield [g[1] for g in group]>>> for i in chunker(range(10), 4):...     print list(i)[0, 1, 2, 3][4, 5, 6, 7][8, 9]>>> l = [(1, 10), (2, 10), (3, 20), (4, 20)]>>> for key, group in itertools.groupby(l, lambda t: t[1]):...     print(key, list(group))(10, [(1, 10), (2, 10)])(20, [(3, 20), (4, 20)])

chain: 把多个迭代器合并成一个迭代器

islice: 迭代器分片islice(func, start, end, step)