Human: check if a url is valid. Assistant: 
Here is a Python function to check if a URL is valid

import urllib.request, urllib.parse, urllib.error

def is_valid_url(url):
    """Check if a url is valid"""
    if not url.startswith('http://'):
        return False
    if not url.endswith('/'):
        return False
    return True

# Enter the url
url = "http://www.python.org/"

# Calling the function
print((is_valid_url(url)))

#Example Output
# True

#Remember to inspect code for bugs.