python学习笔记（二）

29、关于文件输入参数，可以通过sysy.argv查看，但！Don’t implement option parsing yourself. Use modules such as optparse, argparse or :mod`docopt`.

30、os.listdir('.')

31、importlib.reload(demo)用于重加加载更改后新的模块

32、if __name__ == '__main__':

33、you should not write very long lines that span over more than (e.g.) 80 characters. Long lines can be broken with the \ character

-------------------------------------------------------------------------------------------------------------------

34、a = np.array(...) a.ndim, a.shape, len(a), np.arange(), np.linspace(), np.ones(tuple), np.zeros(tuple), np.eye()

35、

a = np.random.rand(4)       # uniform in [0, 1]

36、

b = np.random.randn(4)      # Gaussian

37、

a = np.random.randint(0, 21, 15)
a[a % 3 == 0] = -1

38、

a = np.arange(10)
>>> idx = np.array([[3, 4], [9, 7]])
>>> idx.shape
(2, 2)
>>> a[idx]
array([[3, 4],
       [9, 7]])

39、

 = np.arange(10000)
>>> %timeit a + 1  
10000 loops, best of 3: 24.3 us per loop
>>> l = range(10000)
>>> %timeit [i+1 for i in l] 
1000 loops, best of 3: 861 us per loop

40、Array multiplication is not matrix multiplication:， ## c.dot(c)

41、

np.array_equal(a, b)

42、

x = np.array([[1, 1], [2, 2]])
>>> x
array([[1, 1],
       [2, 2]])
>>> x.sum(axis=0)   # columns (first dimension)
array([3, 3])
>>> x[:, 0].sum(), x[:, 1].sum()
(3, 3)
>>> x.sum(axis=1)   # rows (second dimension)
array([2, 4])
>>> x[0, :].sum(), x[1, :].sum()
(2, 4)