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

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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)