NumPy 从已有数组创建数组

numpy.asarray(a, dtype = None, order = None)

import numpy as np
x =  [1,2,3]
a = np.asarray(x)
print (a)

[1  2  3]

import numpy as np
x =  (1,2,3)
a = np.asarray(x)
print (a)

[1  2  3]

import numpy as np
x =  [(1,2,3),(4,5)]
a = np.asarray(x)
print (a)

[(1, 2, 3) (4, 5)]

import numpy as np
x =  [1,2,3]
a = np.asarray(x, dtype =  float)
print (a)

[ 1.  2.  3.]

numpy.frombuffer(buffer, dtype = float, count = -1, offset = 0)

import numpy as np
s =  b'Hello World'
a = np.frombuffer(s, dtype =  'S1')
print (a)

[b'H' b'e' b'l' b'l' b'o' b' ' b'W' b'o' b'r' b'l' b'd']

import numpy as np
s =  'Hello World'
a = np.frombuffer(s, dtype =  'S1')
print (a)

['H' 'e' 'l' 'l' 'o' ' ' 'W' 'o' 'r' 'l' 'd']

numpy.fromiter(iterable, dtype, count=-1)

import numpy as np 
# 使用 range 函数创建列表对象  
list=range(5)
it=iter(list)
# 使用迭代器创建 ndarray 
x=np.fromiter(it, dtype=float)
print(x)

[0. 1. 2. 3. 4.]