IPython 中的 timeit 和 timeit

分析字符串连接：

In [1]: import string

In [2]: %%timeit s=""; long_list=list(string.ascii_letters)*50
  ....: for substring in long_list:
  ....:   s+=substring
  ....:
1000 loops, best of 3: 570 us per loop

In [3]: %%timeit long_list=list(string.ascii_letters)*50
  ....: s="".join(long_list)
  ....:
100000 loops, best of 3: 16.1 us per loop

分析循环遍历可迭代和列表：

In [4]: %timeit for i in range(100000):pass
100 loops, best of 3: 2.82 ms per loop

In [5]: %timeit for i in list(range(100000)):pass
100 loops, best of 3: 3.95 ms per loop