Read（）函数擦除文件中的文本

Question

我是一个初学的python用户，并且陷入了两难境地。我的程序应该在特定文件中读写。当写入功能起作用时，读取功能只是擦除文件中的所有文本。

def main():
r = open('C:\\Users\\AM\\Desktop\\cool.txt', 'r')
w = open('C:\\Users\\AM\\Desktop\\cool.txt', 'w')
answer = input('Would you like to read or write? (To leave say "quit")')
if(answer == 'read'):
    if(r.mode == 'r'):
        contents = r.read()
        print(contents)
elif(answer == 'write'):
    w.write(input('What would you like to write?'))
    w.close()
elif(answer == 'quit'):
    quit()
else:
    print('Sorry, I do not understand')
main()

感谢您的时间！