Expected type 'PublicFormat', got 'str' instead

在用包cryptography进行非对称加密时, 生成公钥的函数异常.

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import rsa


# 生成RSA密钥对
def generate_rsa_key_pair():
    private_key = rsa.generate_private_key(
        public_exponent=65537,
        key_size=2048,  # 一般是1024位，重要场合是2048位。
        backend=default_backend()
    )
    public_key = private_key.public_key()
    return private_key, public_key


private_key, public_key = generate_rsa_key_pair()


def get_public_key():
    geted_public_key = public_key.public_bytes(
        encoding=serialization.Encoding.PEM,
        format=serialization.PublicFormat.SubjectPublicKeyInfo
    ).decode('utf-8')

    return geted_public_key


"""
        上面的代码块在PyCharm中下面两行
        encoding=serialization.Encoding.PEM,
        format=serialization.PublicFormat.SubjectPublicKeyInfo
        异常： Expected type 'PublicFormat', got 'str' instead
        
        原因： 当时用的cryptography==1.9， cryptography版本太低， 换了一个高版本好了
"""

geted_public_key = get_public_key()
print(f'geted_public_key:\n{geted_public_key}, type:{type(geted_public_key)}')