<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def dshield_ip_check(ip):
 """Checks dshield for info on an IP address"""

    if not is_IPv4Address(ip):
        return None

    headers = {'User-Agent': useragent}
    url = 'https://isc.sans.edu/api/ip/'
    response = requests.get('{0}{1}?json'.format(url, ip), headers=headers)
    return response.json()