title: Regex for matching IPv4 addresses
body: <p>Let's say I have 3 strings:</p>
  
  <pre><code>str1 = 'Hello my name is Ben and my IP address is 127.1.1.1'
  str2 = 'Hello my name is Folks and my IP address is 1.2.3.4.5'
  str3 = 'Hello all, ip addresses: 1.2.3.4.5, 127.1.2.1, 127.2.1.2'
  </code></pre>
  
  <p>I would like to get the following output:</p>
  
  <pre><code>find_ip(str1) #['127.1.1.1']
  find_ip(str2) #[]
  find_ip(str2) #['127.1.2.1', '127.2.1.2']
  </code></pre>
  
  <ol>
  <li>Criteria:
  
  <ul>
  <li>IM addresses with the following form 'x.x.x.x'</li>
  <li>Regex should be <strong>1 group</strong>.</li>
  <li>The number of digits doesn't matter (111.111.111.111) is good.</li>
  </ul></li>
  </ol>
  
  <p>P.S The solution of <a href="https://stackoverflow.com/questions/5284147/validating-ipv4-addresses-with-regexp">this StackOverflow post</a> does <strong>NOT</strong> answer this question.</p>