syder5.3.3抓取网页链接代码运行报错是为什么

在新装的anaconda中的syder5.3.3中运行以下抓取网页中所有网页链接，但运行没有任何反应

import urllib.request, urllib.parse, urllib.error
from bs4 import BeautifulSoup
import ssl

ctx = ssl.create_default_context()
ctx.check_hostname = False
ctx.verify_mode = ssl.CERT_NONE

url = input('Enter - ')
html = urllib.request.urlopen(url, context=ctx).read()
soup = BeautifulSoup(html, 'html.parser')

tags = soup('a')
for tag in tags:
    print(tag.get('href', None))

在consle运行到html = urllib.request.urlopen(url, context=ctx).read()一步时报错，显示：
Traceback (most recent call last):

File "/var/folders/yl/rywwm7wj2v34g4__zdbv4jp80000gn/T/ipykernel_8812/1053319984.py", line 1, in
html = urllib.request.urlopen(url, context=ctx).read()

File "/Users/timcha/opt/anaconda3/lib/python3.9/urllib/request.py", line 214, in urlopen
return opener.open(url, data, timeout)

File "/Users/timcha/opt/anaconda3/lib/python3.9/urllib/request.py", line 501, in open
req = Request(fullurl, data)

File "/Users/timcha/opt/anaconda3/lib/python3.9/urllib/request.py", line 320, in init
self.full_url = url

File "/Users/timcha/opt/anaconda3/lib/python3.9/urllib/request.py", line 346, in full_url
self._parse()

File "/Users/timcha/opt/anaconda3/lib/python3.9/urllib/request.py", line 375, in _parse
raise ValueError("unknown url type: %r" % self.full_url)

ValueError: unknown url type: 'www.baidu.com'

ValueError: unknown url type: 'www.baidu.com'

要加上协议。输入完整的网址 http://www.baidu.com/