AttributeError: 'str' object has no attribute 'isascii'

`AttributeError: 'str' object has no attribute 'isascii'`错误通常是因为在Python 3.7之前的版本中，字符串对象没有isascii()方法。如果你的Python版本低于3.7，那么你需要使用其他方法来检查字符串是否只包含ASCII字符，例如使用正则表达式或自定义函数。

以下是使用正则表达式检查字符串是否只包含ASCII字符的示例代码：

import re

def is_ascii(s):
    return all(ord(c) < 128 for c in s)

def check_ascii(s):
    if is_ascii(s):
        print("The string contains only ASCII characters.")
    else:
        print("The string contains non-ASCII characters.")

s = "Hello, world!"
check_ascii(s) # 输出：The string contains only ASCII characters.

s = "你好，世界！"
check_ascii(s) # 输出：The string contains non-ASCII characters.

如果你的Python版本高于或等于3.7，那么你可以直接使用字符串对象的isascii()方法来检查字符串是否只包含ASCII字符，例如：

s = "Hello, world!"
if s.isascii():
    print("The string contains only ASCII characters.")
else:
    print("The string contains non-ASCII characters.")