python函數的傳參引用

python的函數調用中，将可變類型（list，numpy，等）傳入函數做參數時，是傳位址調用，這樣在函數中修改變量的值時，會改變函數外變量的值

example1

import numpy as np

def func(vertices, scale):
    vertices[[1,3,5,7]] *= scale
    print(vertices)

vertices = np.asarray([0,1,2,3,4,5,6,7])
func(vertices, 3)
print(vertices)

[ 0  3  2  9  4 15  6 21]
[ 0  3  2  9  4 15  6 21]
           

改變了vertices變量的值。

如果不想改變怎麼辦

• 用copy（）屬性，copy（）會傳回同樣值的另外一個位址
• 在函數中建立一個變量，

solution1

import numpy as np

def func(vertices, scale):
    vertices[[1,3,5,7]] *= scale
    print(vertices)

vertices = np.asarray([0,1,2,3,4,5,6,7])
func(vertices.copy(), 3)
print(vertices)

[ 0  3  2  9  4 15  6 21]
[0 1 2 3 4 5 6 7]
           

solution2

import numpy as np

def func(vertices, scale):
    new_vertices = np.zeros(vertices.shape)
    new_vertices[[1,3,5,7]] = vertices[[1,3,5,7]] * scale
    print(vertices)
    print(new_vertices)

vertices = np.asarray([0,1,2,3,4,5,6,7])
func(vertices.copy(), 3)
print(vertices)
[0 1 2 3 4 5 6 7]
[ 0.  3.  0.  9.  0. 15.  0. 21.]
[0 1 2 3 4 5 6 7]