Python 读书笔记

Syntax best practice:

• List Comprehensions
  

  >>>  [i  for  i  in  range( 10 )  if  i  %   2   ==  0]
  
  Enumeration:
  

  >>>  def _treatment(pos, element):
    return  ' %d: %s ' % (pos, element)
  
  >>> seq = [ " one ",  " two ",  " three "]
  >>> [_treatment(i, el)  for i, el  in enumerate(seq)]
  [ ' 0: one ',  ' 1: two ',  ' 2: three ']

  
  Iterators and Generators
  

  >>>  def fibonacci():
   a, b = 0, 1
    while True:
    yield b  # 这里返回 generator，一个特殊的iterator
   a, b = b, a + b
  
  >>> fib = fibonacci()
  >>> fib.next()
  1
  >>> fib.next()
  1
  >>> fib.next()
  2
  >>> [fib.next()  for i  in range(10)]
  [3, 5, 8, 13, 21, 34, 55, 89, 144, 233]

  generators should be considered every time you deal with a

  function that returns a sequence or works in a loop;
  

  It is better to have a lot of simple iterable functions that work over

  sequences of values than a complex function that computes the result for

  one value at a time.

  >>>  def my_generator():
    try:
    yield  ' something '
    except ValueError:
    yield  ' dealing with the exception '
    finally:
    print  " ok let's clean "
  
  >>> gen = my_generator()
  >>> gen.next()
  ' something '
  >>> gen.throw(ValueError( ' mean mean mean '))
  ' dealing with the exception '
  >>> gen.close()
  ok let ' s clean
  >>> gen.next()
  Traceback (most recent call last):
  File  " <stdin> ", line 1,  in <module>
  StopIteration