无法对列表调用max函数

def find_max(lst):
    max_value = lst[0]
    for num in lst:
        if num > max_value:
            max_value = num
    return max_value

# 调用自定义函数
my_list = [1, 5, 3, 9, 2]
max_value = find_max(my_list)
print(max_value)

my_list = [1, 5, 3, 9, 2]
sorted_list = sorted(my_list)
max_value = sorted_list[-1]
print(max_value)

import numpy as np

my_list = [1, 5, 3, 9, 2]
max_value = np.max(my_list)
print(max_value)