可以在明文后面添加填充，使其长度成为16的倍数。

示例代码：

from Crypto.Cipher import AES
import base64

def aes_encrypt(key, data):
    cipher = AES.new(key.encode("utf8"), AES.MODE_ECB)
    data = data.encode("utf8")
    # 填充
    pad_len = 16 - len(data) % 16
    data += pad_len * chr(pad_len).encode()
    ciphertext = cipher.encrypt(data)
    return base64.b64encode(ciphertext).decode()

def aes_decrypt(key, data):
    cipher = AES.new(key.encode("utf8"), AES.MODE_ECB)
    ciphertext = base64.b64decode(data)
    plaintext = cipher.decrypt(ciphertext)
    # 去除填充
    pad_len = plaintext[-1]
    plaintext = plaintext[:-pad_len]
    return plaintext.decode()