markup fiddling

regular-expressions.html

@@ -311,7 +311,7 @@ body{counter-reset:h1 5}
   File "<stdin>", line 1, in <module>
 AttributeError: 'NoneType' object has no attribute 'groups'</samp></pre>
 <ol>
-<li>Always read regular expressions from left to right. This one matches the beginning of the string, and then <code>(\d{3})</code>. What&#8217;s <code>\d{3}</code>?  Well, <code>\d</code> means &#8220;any numeric digit&#8221; (<code>0</code> through <code>9</code>). The <code>{3}</code> means &#8220;match exactly three numeric digits&#8221;; it&#8217;s a variation on the <a href=#nmsyntax><code>{n,m} syntax</code></a> you saw earlier. Putting it all in parentheses means &#8220;match exactly three numeric digits, <em>and then remember them as a group that I can ask for later</em>&#8221;. Then match a literal hyphen. Then match another group of exactly three digits. Then another literal hyphen. Then another group of exactly four digits. Then match the end of the string.
+<li>Always read regular expressions from left to right. This one matches the beginning of the string, and then <code>(\d{3})</code>. What&#8217;s <code>\d{3}</code>?  Well, <code>\d</code> means &#8220;any numeric digit&#8221; (0 through <code>9</code>). The <code>{3}</code> means &#8220;match exactly three numeric digits&#8221;; it&#8217;s a variation on the <a href=#nmsyntax><code>{n,m} syntax</code></a> you saw earlier. Putting it all in parentheses means &#8220;match exactly three numeric digits, <em>and then remember them as a group that I can ask for later</em>&#8221;. Then match a literal hyphen. Then match another group of exactly three digits. Then another literal hyphen. Then another group of exactly four digits. Then match the end of the string.
 <li>To get access to the groups that the regular expression parser remembered along the way, use the <code>groups()</code> method on the object that the <code>search()</code> method returns. It will return a tuple of however many groups were defined in the regular expression. In this case, you defined three groups, one with three digits, one with three digits, and one with four digits.
 <li>This regular expression is not the final answer, because it doesn&#8217;t handle a phone number with an extension on the end. For that, you&#8217;ll need to expand the regular expression.
 <li>And this is why you should never &#8220;chain&#8221; the <code>search()</code> and <code>groups()</code> methods in production code. If the <code>search()</code> method returns no matches, it returns <a href=native-datatypes.html#none><code>None</code></a>, not a regular expression match object. Calling <code>None.groups()</code> raises a perfectly obvious exception: <code>None</code> doesn&#8217;t have a <code>groups()</code> method. (Of course, it&#8217;s slightly less obvious when you get this exception from deep within your code. Yes, I speak from experience here.)