added 32nd Python tip

Author: learnbyexample

Diff for: README.md

@@ -69,6 +69,7 @@ I'm addicted to reading fantasy/sci-fi books, so I have a [blog](https://learnby
 
 ## Tips
 
+* [Python tip 32: positive lookarounds](https://learnbyexample.github.io/tips/python-tip-32/)
 * [Vim tip 30: some general Vim settings](https://learnbyexample.github.io/tips/vim-tip-30/)
 * [CLI tip 31: concatenate files column wise](https://learnbyexample.github.io/tips/cli-tip-31/)
 * [Python tip 31: next() function](https://learnbyexample.github.io/tips/python-tip-31/)

Diff for: atom.xml

@@ -5,8 +5,57 @@
 	<link href="https://learnbyexample.github.io/atom.xml" rel="self" type="application/atom+xml"/>
   <link href="https://learnbyexample.github.io"/>
 	<generator uri="https://www.getzola.org/">Zola</generator>
-	<updated>2023-08-08T00:00:00+00:00</updated>
+	<updated>2023-08-16T00:00:00+00:00</updated>
 	<id>https://learnbyexample.github.io/atom.xml</id>
+	<entry xml:lang="en">
+		<title>Python tip 32: positive lookarounds</title>
+		<published>2023-08-16T00:00:00+00:00</published>
+		<updated>2023-08-16T00:00:00+00:00</updated>
+		<link rel="alternate" href="https://learnbyexample.github.io/tips/python-tip-32/" type="text/html"/>
+		<id>https://learnbyexample.github.io/tips/python-tip-32/</id>
+		<content type="html">&lt;p&gt;Lookarounds help to create custom anchors and add conditions within a regex definition. These assertions are also known as &lt;strong&gt;zero-width patterns&lt;&#x2F;strong&gt; because they add restrictions similar to anchors and are not part of the matched portions. Negative lookarounds were discussed in &lt;a href=&quot;https:&#x2F;&#x2F;learnbyexample.github.io&#x2F;tips&#x2F;python-tip-29&#x2F;&quot;&gt;this post&lt;&#x2F;a&gt;. The syntax for positive lookarounds is shown below:&lt;&#x2F;p&gt;
+&lt;ul&gt;
+&lt;li&gt;&lt;code&gt;(?=pat)&lt;&#x2F;code&gt; positive lookahead assertion&lt;&#x2F;li&gt;
+&lt;li&gt;&lt;code&gt;(?&amp;lt;=pat)&lt;&#x2F;code&gt; positive lookbehind assertion&lt;&#x2F;li&gt;
+&lt;&#x2F;ul&gt;
+&lt;p&gt;Here are some examples:&lt;&#x2F;p&gt;
+&lt;pre data-lang=&quot;python&quot; style=&quot;background-color:#f5f5f5;color:#1f1f1f;&quot; class=&quot;language-python &quot;&gt;&lt;code class=&quot;language-python&quot; data-lang=&quot;python&quot;&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;&amp;gt;&amp;gt;&amp;gt; &lt;&#x2F;span&gt;&lt;span&gt;s &lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;= &lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;42 apple-5, fig3; x-83, y-20: f12&amp;#39;
+&lt;&#x2F;span&gt;&lt;span&gt;
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7f8989;&quot;&gt;# extract digits only if it is followed by ,
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7f8989;&quot;&gt;# note that end of string doesn&amp;#39;t qualify as this is a positive assertion
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;&amp;gt;&amp;gt;&amp;gt; &lt;&#x2F;span&gt;&lt;span&gt;re.&lt;&#x2F;span&gt;&lt;span style=&quot;color:#5597d6;&quot;&gt;findall&lt;&#x2F;span&gt;&lt;span&gt;(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#668f14;&quot;&gt;r&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;\d&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;?=&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;,)&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;, s)
+&lt;&#x2F;span&gt;&lt;span&gt;[&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;5&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;, &lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;83&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;]
+&lt;&#x2F;span&gt;&lt;span&gt;
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7f8989;&quot;&gt;# extract digits only if it is preceded by - and followed by ; or :
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;&amp;gt;&amp;gt;&amp;gt; &lt;&#x2F;span&gt;&lt;span&gt;re.&lt;&#x2F;span&gt;&lt;span style=&quot;color:#5597d6;&quot;&gt;findall&lt;&#x2F;span&gt;&lt;span&gt;(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#668f14;&quot;&gt;r&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;?&amp;lt;=&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;-)&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;\d&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;?=[:;]&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;)&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;, s)
+&lt;&#x2F;span&gt;&lt;span&gt;[&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;20&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;]
+&lt;&#x2F;span&gt;&lt;span&gt;
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7f8989;&quot;&gt;# replace &amp;#39;par&amp;#39; as long as &amp;#39;part&amp;#39; occurs as a whole word later in the line
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;&amp;gt;&amp;gt;&amp;gt; &lt;&#x2F;span&gt;&lt;span&gt;re.&lt;&#x2F;span&gt;&lt;span style=&quot;color:#5597d6;&quot;&gt;sub&lt;&#x2F;span&gt;&lt;span&gt;(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#668f14;&quot;&gt;r&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;par(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;?=.&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;*\b&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;part&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;\b&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;)&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;, &lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;[&lt;&#x2F;span&gt;&lt;span style=&quot;text-decoration:underline;font-style:italic;color:#d2a8a1;&quot;&gt;\g&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;lt;0&amp;gt;]&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;, &lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;par spare part party&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;)
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;[par] s[par]e part party&amp;#39;
+&lt;&#x2F;span&gt;&lt;&#x2F;code&gt;&lt;&#x2F;pre&gt;
+&lt;p&gt;With lookbehind assertion (both positive and negative), the pattern used for the assertion cannot &lt;em&gt;imply&lt;&#x2F;em&gt; matching variable length of text. Fixed length quantifier is allowed. Different length alternations are not allowed, even if the individual alternations are of fixed length.&lt;&#x2F;p&gt;
+&lt;pre data-lang=&quot;python&quot; style=&quot;background-color:#f5f5f5;color:#1f1f1f;&quot; class=&quot;language-python &quot;&gt;&lt;code class=&quot;language-python&quot; data-lang=&quot;python&quot;&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;&amp;gt;&amp;gt;&amp;gt; &lt;&#x2F;span&gt;&lt;span&gt;s &lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;= &lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;pore42 tar3 dare7 care5&amp;#39;
+&lt;&#x2F;span&gt;&lt;span&gt;
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7f8989;&quot;&gt;# not allowed
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;&amp;gt;&amp;gt;&amp;gt; &lt;&#x2F;span&gt;&lt;span&gt;re.&lt;&#x2F;span&gt;&lt;span style=&quot;color:#5597d6;&quot;&gt;findall&lt;&#x2F;span&gt;&lt;span&gt;(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#668f14;&quot;&gt;r&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;?&amp;lt;=&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;tar&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;|&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;dare)&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;\d&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;, s)
+&lt;&#x2F;span&gt;&lt;span&gt;re.error: look&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;-&lt;&#x2F;span&gt;&lt;span&gt;behind requires fixed&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;-&lt;&#x2F;span&gt;&lt;span&gt;width pattern
+&lt;&#x2F;span&gt;&lt;span&gt;
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7f8989;&quot;&gt;# workaround for r&amp;#39;(?&amp;lt;!tar|dare)\d+&amp;#39;
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;&amp;gt;&amp;gt;&amp;gt; &lt;&#x2F;span&gt;&lt;span&gt;re.&lt;&#x2F;span&gt;&lt;span style=&quot;color:#5597d6;&quot;&gt;findall&lt;&#x2F;span&gt;&lt;span&gt;(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#668f14;&quot;&gt;r&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;?&amp;lt;!&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;tar)(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;?&amp;lt;!&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;dare)&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;\d&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;, s)
+&lt;&#x2F;span&gt;&lt;span&gt;[&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;42&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;, &lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;5&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;]
+&lt;&#x2F;span&gt;&lt;span&gt;
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7f8989;&quot;&gt;# workaround for r&amp;#39;(?&amp;lt;=tar|dare)\d+&amp;#39;
+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;&amp;gt;&amp;gt;&amp;gt; &lt;&#x2F;span&gt;&lt;span&gt;re.&lt;&#x2F;span&gt;&lt;span style=&quot;color:#5597d6;&quot;&gt;findall&lt;&#x2F;span&gt;&lt;span&gt;(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#668f14;&quot;&gt;r&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;(?:(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;?&amp;lt;=&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;tar)&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;|&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;(&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;?&amp;lt;=&lt;&#x2F;span&gt;&lt;span style=&quot;color:#7c8f4c;&quot;&gt;dare))&lt;&#x2F;span&gt;&lt;span style=&quot;color:#aeb52b;&quot;&gt;\d&lt;&#x2F;span&gt;&lt;span style=&quot;color:#72ab00;&quot;&gt;+&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;, s)
+&lt;&#x2F;span&gt;&lt;span&gt;[&lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;3&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;, &lt;&#x2F;span&gt;&lt;span style=&quot;color:#d07711;&quot;&gt;&amp;#39;7&amp;#39;&lt;&#x2F;span&gt;&lt;span&gt;]
+&lt;&#x2F;span&gt;&lt;&#x2F;code&gt;&lt;&#x2F;pre&gt;
+&lt;p&gt;&lt;img src=&quot;&#x2F;images&#x2F;info.svg&quot; alt=&quot;info&quot; &#x2F;&gt; The third-party &lt;code&gt;regex&lt;&#x2F;code&gt; module (&lt;a href=&quot;https:&#x2F;&#x2F;pypi.org&#x2F;project&#x2F;regex&#x2F;&quot;&gt;https:&#x2F;&#x2F;pypi.org&#x2F;project&#x2F;regex&#x2F;&lt;&#x2F;a&gt;) offers advanced features like variable-length lookbehinds, subexpression calls, etc.&lt;&#x2F;p&gt;
+&lt;p&gt;&lt;strong&gt;Video demo&lt;&#x2F;strong&gt;:&lt;&#x2F;p&gt;
+&lt;p align=&quot;center&quot;&gt;&lt;iframe width=&quot;560&quot; height=&quot;315&quot; loading=&quot;lazy&quot; src=&quot;https:&#x2F;&#x2F;www.youtube.com&#x2F;embed&#x2F;Bu27WS-GExk&quot; title=&quot;YouTube video player&quot; frameborder=&quot;0&quot; allow=&quot;accelerometer; clipboard-write; encrypted-media; gyroscope; picture-in-picture&quot; allowfullscreen&gt;&lt;&#x2F;iframe&gt;&lt;&#x2F;p&gt;
+&lt;br&gt;
+&lt;p&gt;&lt;img src=&quot;&#x2F;images&#x2F;info.svg&quot; alt=&quot;info&quot; &#x2F;&gt; See also my &lt;a href=&quot;https:&#x2F;&#x2F;github.com&#x2F;learnbyexample&#x2F;100_page_python_intro&quot;&gt;100 Page Python Intro&lt;&#x2F;a&gt; and &lt;a href=&quot;https:&#x2F;&#x2F;github.com&#x2F;learnbyexample&#x2F;py_regular_expressions&quot;&gt;Understanding Python re(gex)?&lt;&#x2F;a&gt; ebooks.&lt;&#x2F;p&gt;
+</content>
+	</entry>
 	<entry xml:lang="en">
 		<title>Vim tip 30: some general Vim settings</title>
 		<published>2023-08-08T00:00:00+00:00</published>

Diff for: sitemap.xml

@@ -435,7 +435,7 @@
     </url>
     <url>
         <loc>https://learnbyexample.github.io/tips/</loc>
-        <lastmod>2023-08-08</lastmod>
+        <lastmod>2023-08-16</lastmod>
     </url>
     <url>
         <loc>https://learnbyexample.github.io/tips/cli-tip-1/</loc>
@@ -661,6 +661,10 @@
         <loc>https://learnbyexample.github.io/tips/python-tip-31/</loc>
         <lastmod>2023-07-25</lastmod>
     </url>
+    <url>
+        <loc>https://learnbyexample.github.io/tips/python-tip-32/</loc>
+        <lastmod>2023-08-16</lastmod>
+    </url>
     <url>
         <loc>https://learnbyexample.github.io/tips/python-tip-4/</loc>
         <lastmod>2022-06-10</lastmod>