1，解决办法
 "C:\\Users\\Darkness-02\\Desktop\\test.txt"

多加一个反斜杠就行了

2，解决办法
r"C:\Users\Darkness-02\Desktop\txt.txt"
变为字符串

玩具

with open("C:\\Users\\Darkness-02\\Desktop\\test.txt","r") as txt:
    print(txt.read())

with open(r"C:\Users\Darkness-02\Desktop\txt.txt","r") as txt:
    print(txt.read())