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    <title>DEV Community: Harsh Thalwal</title>
    <description>The latest articles on DEV Community by Harsh Thalwal (@harsh_thalwal_d1262cc3a90).</description>
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    <item>
      <title>Rust vs C: Who is really better?</title>
      <dc:creator>Harsh Thalwal</dc:creator>
      <pubDate>Mon, 10 Nov 2025 10:57:48 +0000</pubDate>
      <link>https://dev.to/harsh_thalwal_d1262cc3a90/rust-vs-c-a-balanced-look-at-performance-safety-and-the-future-of-systems-programming-pp6</link>
      <guid>https://dev.to/harsh_thalwal_d1262cc3a90/rust-vs-c-a-balanced-look-at-performance-safety-and-the-future-of-systems-programming-pp6</guid>
      <description>&lt;p&gt;For decades, &lt;strong&gt;C&lt;/strong&gt; has been the backbone of systems programming — powering everything from operating systems to embedded chips. But in the last few years, a new challenger, &lt;strong&gt;Rust&lt;/strong&gt;, has risen with a bold promise: &lt;em&gt;the performance of C without the memory bugs.&lt;/em&gt;&lt;/p&gt;

&lt;p&gt;So, in this era of safer and faster programming, the question is — &lt;strong&gt;who wins: Rust or C?&lt;/strong&gt;&lt;/p&gt;




&lt;h2&gt;
  
  
  The Legacy of C
&lt;/h2&gt;

&lt;p&gt;C is the language that built the modern computing world. Created in the 1970s at Bell Labs, it’s behind &lt;strong&gt;UNIX&lt;/strong&gt;, &lt;strong&gt;Linux&lt;/strong&gt;, and most &lt;strong&gt;device firmware&lt;/strong&gt;.&lt;/p&gt;

&lt;p&gt;Developers love C for its &lt;strong&gt;speed, portability, and direct control&lt;/strong&gt; over hardware. You know exactly what the machine is doing, line by line. But that power also comes with danger — memory leaks, segmentation faults, and buffer overflows have haunted C developers for decades.&lt;/p&gt;

&lt;p&gt;Still, C’s simplicity and predictability made it irreplaceable — until Rust arrived.&lt;/p&gt;




&lt;h2&gt;
  
  
  The Rise of Rust
&lt;/h2&gt;

&lt;p&gt;Rust, born at Mozilla in the 2010s, set out to fix what C could not: &lt;strong&gt;memory safety without performance loss.&lt;/strong&gt;&lt;/p&gt;

&lt;p&gt;It introduced a powerful &lt;strong&gt;ownership system&lt;/strong&gt;, where the compiler enforces strict rules about who owns and accesses memory. This prevents common errors like dangling pointers or data races &lt;em&gt;before&lt;/em&gt; your program even runs.&lt;/p&gt;

&lt;p&gt;In short — if your Rust code compiles, it’s probably safe.&lt;/p&gt;

&lt;p&gt;And unlike garbage-collected languages like Java or Python, Rust doesn’t rely on a runtime to manage memory. You get &lt;strong&gt;C-like performance&lt;/strong&gt; with far fewer crashes.&lt;/p&gt;




&lt;h2&gt;
  
  
  Performance and Safety: Head to Head
&lt;/h2&gt;

&lt;p&gt;Both C and Rust compile to machine code, so performance-wise, they’re neck and neck.&lt;/p&gt;

&lt;p&gt;However, Rust takes the edge when it comes to &lt;strong&gt;concurrent programming&lt;/strong&gt; — it makes sure your threads don’t access the same data in unsafe ways. In C, that’s entirely up to you (and your debugging skills).&lt;/p&gt;

&lt;p&gt;Rust’s biggest win is &lt;strong&gt;memory safety&lt;/strong&gt;. Where C demands discipline, Rust enforces it automatically. You spend less time tracking bugs and more time building actual features.&lt;/p&gt;




&lt;h2&gt;
  
  
  Developer Experience
&lt;/h2&gt;

&lt;p&gt;C is minimalist — you can learn it quickly, but mastering it safely takes years. Rust is the opposite: it’s &lt;strong&gt;harder to learn&lt;/strong&gt;, but once you grasp it, it feels empowering.&lt;/p&gt;

&lt;p&gt;The &lt;strong&gt;Rust compiler&lt;/strong&gt; is famously strict but extremely helpful. With tools like &lt;strong&gt;Cargo&lt;/strong&gt; (package manager) and &lt;strong&gt;Clippy&lt;/strong&gt; (linter), writing modern, maintainable code is easier than ever.&lt;/p&gt;

&lt;p&gt;It’s not rare to see developers say, &lt;em&gt;“Rust made me a better programmer.”&lt;/em&gt;&lt;/p&gt;




&lt;h2&gt;
  
  
  Use Cases and Ecosystem
&lt;/h2&gt;

&lt;ul&gt;
&lt;li&gt;
&lt;strong&gt;C excels in:&lt;/strong&gt; operating systems, embedded systems, compilers, and hardware-level programming.&lt;/li&gt;
&lt;li&gt;
&lt;strong&gt;Rust excels in:&lt;/strong&gt; web servers, game engines, blockchain, and safety-critical systems.&lt;/li&gt;
&lt;/ul&gt;

&lt;p&gt;Big names like &lt;strong&gt;Microsoft&lt;/strong&gt;, &lt;strong&gt;Google&lt;/strong&gt;, and &lt;strong&gt;Amazon&lt;/strong&gt; are already integrating Rust into their core infrastructure — often replacing old C/C++ modules for better security and reliability.&lt;/p&gt;

&lt;p&gt;That says a lot about where the industry is heading.&lt;/p&gt;




&lt;h2&gt;
  
  
  Verdict: Not Rivals, but Partners
&lt;/h2&gt;

&lt;p&gt;So, who wins — Rust or C?&lt;/p&gt;

&lt;p&gt;It’s not really a battle. &lt;strong&gt;C&lt;/strong&gt; remains unbeatable for ultra-low-level tasks and legacy systems. But &lt;strong&gt;Rust&lt;/strong&gt; is the natural successor for projects that demand both &lt;strong&gt;speed and safety&lt;/strong&gt;.&lt;/p&gt;

&lt;p&gt;In truth, Rust doesn’t want to replace C — it wants to &lt;strong&gt;evolve&lt;/strong&gt; it.&lt;br&gt;
One built the digital world; the other is making it safer.&lt;/p&gt;




&lt;h3&gt;
  
  
  Final Thoughts
&lt;/h3&gt;

&lt;p&gt;Rust and C aren’t enemies — they’re milestones.&lt;br&gt;
C gave us control; Rust gives us confidence.&lt;/p&gt;

&lt;p&gt;In the end, the best developers aren’t the ones who pick sides. They’re the ones who know &lt;strong&gt;when to use which.&lt;/strong&gt;&lt;/p&gt;

</description>
      <category>rustvsc</category>
      <category>rust</category>
      <category>rustmemorysafety</category>
      <category>whichisbetter</category>
    </item>
    <item>
      <title>Beginner friendly Postfix-Prefix tutorial for CLI Calculator in Python.</title>
      <dc:creator>Harsh Thalwal</dc:creator>
      <pubDate>Thu, 23 Jan 2025 18:30:00 +0000</pubDate>
      <link>https://dev.to/harsh_thalwal_d1262cc3a90/beginner-friendly-postfix-prefix-tutorial-for-cli-calculator-in-python-5a38</link>
      <guid>https://dev.to/harsh_thalwal_d1262cc3a90/beginner-friendly-postfix-prefix-tutorial-for-cli-calculator-in-python-5a38</guid>
      <description>&lt;p&gt;Hello everyone!👋&lt;br&gt;
I’m sure you’ve all seen many simple calculator tutorials online—whether on YouTube, other social media, or well you get the idea! There are tons of beginner-friendly calculator tutorials out there, but most are limited to something like this:&lt;br&gt;
&lt;/p&gt;

&lt;div class="highlight js-code-highlight"&gt;
&lt;pre class="highlight shell"&gt;&lt;code&gt;Enter n1 : 2
Enter n2 : 3
Enter operator &lt;span class="o"&gt;(&lt;/span&gt;+,-,&lt;span class="k"&gt;*&lt;/span&gt;,/&lt;span class="o"&gt;)&lt;/span&gt; : +
Result : 5
&lt;/code&gt;&lt;/pre&gt;

&lt;/div&gt;



&lt;p&gt;As a coder and user, I found this approach a bit tedious. Entering numbers and operators separately feels clunky and restricts you from solving more complex expressions quickly. So, I thought, why not create a simple yet powerful calculator that can handle full mathematical expressions in one go? Something like this:&lt;br&gt;
&lt;/p&gt;

&lt;div class="highlight js-code-highlight"&gt;
&lt;pre class="highlight python"&gt;&lt;code&gt;&lt;span class="n"&gt;Enter&lt;/span&gt; &lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="mi"&gt;23&lt;/span&gt; &lt;span class="o"&gt;-&lt;/span&gt; &lt;span class="mi"&gt;21&lt;/span&gt; &lt;span class="o"&gt;*&lt;/span&gt; &lt;span class="mi"&gt;32&lt;/span&gt; &lt;span class="o"&gt;/&lt;/span&gt; &lt;span class="mi"&gt;34&lt;/span&gt; &lt;span class="o"&gt;+&lt;/span&gt; &lt;span class="mi"&gt;1000&lt;/span&gt;
&lt;span class="n"&gt;Result&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="mf"&gt;1003.2352941176471&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;

&lt;/div&gt;



&lt;p&gt;I won’t say it’s perfect (don’t worry — the answer is correct!), but I really like how it lets me enter full expressions naturally. Plus, it’s a fun challenge to flex my problem-solving skills 😅. In this blog, I’ll share how I built this calculator, the hurdles I faced, and how you can create your own to tackle complex math with ease!&lt;/p&gt;

&lt;p&gt;In this tutorial, I’ll keep things simple. There will still be room for improvement — and that part is up to you!&lt;br&gt;&lt;br&gt;
So, let’s get started! 🚀&lt;/p&gt;

&lt;p&gt;&lt;strong&gt;The plan was quite simple.&lt;/strong&gt;&lt;/p&gt;

&lt;ol&gt;
&lt;li&gt;&lt;p&gt;Take the user input, which would be an infix expression (something like this :- 2+1-2+32).&lt;/p&gt;&lt;/li&gt;
&lt;li&gt;&lt;p&gt;Convert it into postfix. Which would look like this : [ 2,1,2,32,+,-,+ ].&lt;/p&gt;&lt;/li&gt;
&lt;li&gt;&lt;p&gt;And then solve it. How? It’s explained later in this blog post.&lt;/p&gt;&lt;/li&gt;
&lt;/ol&gt;
&lt;h1&gt;
  
  
  1. Taking the user input.
&lt;/h1&gt;


&lt;div class="highlight js-code-highlight"&gt;
&lt;pre class="highlight python"&gt;&lt;code&gt;&lt;span class="k"&gt;def&lt;/span&gt; &lt;span class="nf"&gt;main&lt;/span&gt;&lt;span class="p"&gt;():&lt;/span&gt;
    &lt;span class="n"&gt;valid_inputs&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;0&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;1&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;2&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;3&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;4&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;5&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;6&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;7&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;8&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;9&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;+&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;-&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;*&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;/&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;]&lt;/span&gt;
    &lt;span class="k"&gt;try&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
        &lt;span class="n"&gt;user_input&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="nf"&gt;input&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;Enter : &lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
        &lt;span class="n"&gt;user_input&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="n"&gt;user_input&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;replace&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="sh"&gt;"&lt;/span&gt;&lt;span class="s"&gt; &lt;/span&gt;&lt;span class="sh"&gt;"&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;""&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
        &lt;span class="k"&gt;for&lt;/span&gt; &lt;span class="n"&gt;char&lt;/span&gt; &lt;span class="ow"&gt;in&lt;/span&gt; &lt;span class="n"&gt;user_input&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
            &lt;span class="k"&gt;if&lt;/span&gt; &lt;span class="n"&gt;char&lt;/span&gt; &lt;span class="ow"&gt;not&lt;/span&gt; &lt;span class="ow"&gt;in&lt;/span&gt; &lt;span class="n"&gt;valid_inputs&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
                &lt;span class="k"&gt;raise&lt;/span&gt; &lt;span class="nc"&gt;ValueError&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="sh"&gt;"&lt;/span&gt;&lt;span class="s"&gt;Invalid input&lt;/span&gt;&lt;span class="sh"&gt;"&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
    &lt;span class="k"&gt;except&lt;/span&gt; &lt;span class="nb"&gt;Exception&lt;/span&gt; &lt;span class="k"&gt;as&lt;/span&gt; &lt;span class="n"&gt;e&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
        &lt;span class="nf"&gt;print&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;e&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
        &lt;span class="k"&gt;return&lt;/span&gt;
    &lt;span class="nf"&gt;userinput_to_infix_generator&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;user_input&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
&lt;span class="k"&gt;if&lt;/span&gt; &lt;span class="n"&gt;__name__&lt;/span&gt; &lt;span class="o"&gt;==&lt;/span&gt; &lt;span class="sh"&gt;"&lt;/span&gt;&lt;span class="s"&gt;__main__&lt;/span&gt;&lt;span class="sh"&gt;"&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
    &lt;span class="nf"&gt;main&lt;/span&gt;&lt;span class="p"&gt;()&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;

&lt;/div&gt;


&lt;p&gt;Inside the main() function I did two things.&lt;/p&gt;

&lt;ol&gt;
&lt;li&gt;&lt;p&gt;Taking the user input.&lt;/p&gt;&lt;/li&gt;
&lt;li&gt;&lt;p&gt;Making sure that it was a valid input.&lt;/p&gt;&lt;/li&gt;
&lt;/ol&gt;

&lt;p&gt;If there is problem with the expressions like having an invalid symbol the code immediately raises a value error.&lt;br&gt;
&lt;/p&gt;

&lt;div class="highlight js-code-highlight"&gt;
&lt;pre class="highlight python"&gt;&lt;code&gt;&lt;span class="n"&gt;valid_inputs&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;0&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;1&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;2&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;3&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;4&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;5&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;6&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;7&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;8&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;9&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;+&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;-&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;*&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;/&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;]&lt;/span&gt;
    &lt;span class="k"&gt;try&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
        &lt;span class="n"&gt;user_input&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="nf"&gt;input&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;Enter : &lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
        &lt;span class="n"&gt;user_input&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="n"&gt;user_input&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;replace&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="sh"&gt;"&lt;/span&gt;&lt;span class="s"&gt; &lt;/span&gt;&lt;span class="sh"&gt;"&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt;&lt;span class="sh"&gt;""&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
        &lt;span class="k"&gt;for&lt;/span&gt; &lt;span class="n"&gt;char&lt;/span&gt; &lt;span class="ow"&gt;in&lt;/span&gt; &lt;span class="n"&gt;user_input&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="o"&gt;&amp;lt;-----&lt;/span&gt;
            &lt;span class="k"&gt;if&lt;/span&gt; &lt;span class="n"&gt;char&lt;/span&gt; &lt;span class="ow"&gt;not&lt;/span&gt; &lt;span class="ow"&gt;in&lt;/span&gt; &lt;span class="n"&gt;valid_inputs&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
                &lt;span class="k"&gt;raise&lt;/span&gt; &lt;span class="nc"&gt;ValueError&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="sh"&gt;"&lt;/span&gt;&lt;span class="s"&gt;Invalid input&lt;/span&gt;&lt;span class="sh"&gt;"&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
    &lt;span class="k"&gt;except&lt;/span&gt; &lt;span class="nb"&gt;Exception&lt;/span&gt; &lt;span class="k"&gt;as&lt;/span&gt; &lt;span class="n"&gt;e&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
        &lt;span class="nf"&gt;print&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;e&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
        &lt;span class="k"&gt;return&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;

&lt;/div&gt;



&lt;p&gt;The loop checks each character (&lt;code&gt;char&lt;/code&gt;) from the user's input. If any character isn't in the &lt;code&gt;valid_inputs&lt;/code&gt; list, a &lt;code&gt;ValueError&lt;/code&gt;is raised. If all characters are valid, the code moves on to the next step.&lt;/p&gt;

&lt;p&gt;Once it’s done with comparison and it was a success. It calls the function &lt;code&gt;userinput_to_infix_generator(user_input)&lt;/code&gt; with &lt;code&gt;user_input&lt;/code&gt; as argument.&lt;/p&gt;

&lt;p&gt;The &lt;code&gt;userinput_to_infix_generator(user_input)&lt;/code&gt; function takes the clean input and turns it into a list of tokens we can later convert from infix to postfix.&lt;/p&gt;

&lt;p&gt;You're right! Here's your full section rewritten cleanly in &lt;strong&gt;Markdown&lt;/strong&gt;, with everything from your original idea included, and polished for clarity and readability — all ready to be pasted into your blog:&lt;/p&gt;

&lt;h2&gt;
  
  
  &lt;code&gt;userinput_to_infix_generator(user_input)&lt;/code&gt;
&lt;/h2&gt;

&lt;p&gt;The code itself isn’t very complex — it just turns the &lt;code&gt;user_input&lt;/code&gt; string into a list called &lt;code&gt;infix&lt;/code&gt;, where each number and operator is stored as a separate item.&lt;br&gt;
&lt;/p&gt;

&lt;div class="highlight js-code-highlight"&gt;
&lt;pre class="highlight python"&gt;&lt;code&gt;&lt;span class="k"&gt;def&lt;/span&gt; &lt;span class="nf"&gt;userinput_to_infix_generator&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;user_input&lt;/span&gt;&lt;span class="p"&gt;):&lt;/span&gt;
    &lt;span class="n"&gt;infix&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="p"&gt;[]&lt;/span&gt;
    &lt;span class="n"&gt;temp&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="sh"&gt;""&lt;/span&gt;
    &lt;span class="n"&gt;symbols&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;+&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;-&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;/&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;*&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;]&lt;/span&gt;
    &lt;span class="k"&gt;for&lt;/span&gt; &lt;span class="n"&gt;i&lt;/span&gt; &lt;span class="ow"&gt;in&lt;/span&gt; &lt;span class="n"&gt;user_input&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;&lt;span class="o"&gt;&amp;lt;-------&lt;/span&gt;
        &lt;span class="k"&gt;if&lt;/span&gt; &lt;span class="n"&gt;i&lt;/span&gt; &lt;span class="ow"&gt;not&lt;/span&gt; &lt;span class="ow"&gt;in&lt;/span&gt; &lt;span class="n"&gt;symbols&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
            &lt;span class="n"&gt;temp&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="n"&gt;temp&lt;/span&gt; &lt;span class="o"&gt;+&lt;/span&gt; &lt;span class="n"&gt;i&lt;/span&gt;
        &lt;span class="k"&gt;else&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
            &lt;span class="n"&gt;infix&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;append&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;temp&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
            &lt;span class="n"&gt;infix&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;append&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;i&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
            &lt;span class="n"&gt;temp&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="sh"&gt;""&lt;/span&gt;
    &lt;span class="k"&gt;if&lt;/span&gt; &lt;span class="n"&gt;temp&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
        &lt;span class="n"&gt;infix&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;append&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;temp&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
    &lt;span class="nf"&gt;infix_to_postfix&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;infix&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;

&lt;/div&gt;



&lt;p&gt;The key part of this function is how it handles the input when numbers are written together without clear spaces — for example, &lt;code&gt;223+32&lt;/code&gt;. We don't want to treat &lt;code&gt;'2'&lt;/code&gt;, &lt;code&gt;'2'&lt;/code&gt;, and &lt;code&gt;'3'&lt;/code&gt; as separate characters. Instead, we need to combine them into a full number like &lt;code&gt;"223"&lt;/code&gt; and then store it in the list.&lt;/p&gt;

&lt;p&gt;This is handled inside the loop:&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;&lt;p&gt;If the character is &lt;strong&gt;not&lt;/strong&gt; an operator (&lt;code&gt;+&lt;/code&gt;, &lt;code&gt;-&lt;/code&gt;, &lt;code&gt;*&lt;/code&gt;, &lt;code&gt;/&lt;/code&gt;), it's added to a temporary string &lt;code&gt;temp&lt;/code&gt;.&lt;/p&gt;&lt;/li&gt;
&lt;li&gt;&lt;p&gt;When an operator is found, the function:&lt;/p&gt;&lt;/li&gt;
&lt;/ul&gt;

&lt;div class="highlight js-code-highlight"&gt;
&lt;pre class="highlight plaintext"&gt;&lt;code&gt;1. Adds the number stored in `temp` to the `infix` list,

2. Then adds the operator,

3. And resets `temp` for the next number.
&lt;/code&gt;&lt;/pre&gt;

&lt;/div&gt;

&lt;p&gt;Finally, after the loop ends, if &lt;code&gt;temp&lt;/code&gt; still holds the last number, it adds that to the list too.&lt;/p&gt;

&lt;h2&gt;
  
  
  Example:
&lt;/h2&gt;

&lt;p&gt;For input: &lt;code&gt;12+7*5&lt;/code&gt; The resulting &lt;code&gt;infix&lt;/code&gt; list would be: &lt;code&gt;['12', '+', '7', '*', '5']&lt;/code&gt;&lt;/p&gt;

&lt;h1&gt;
  
  
  2. Convert it to postfix
&lt;/h1&gt;

&lt;p&gt;Alright, now that we’ve turned our input string into a nice clean list (our &lt;code&gt;infix&lt;/code&gt; expression), the next step is to convert that into postfix format. This part is super important — because computers find postfix (also known as Reverse Polish Notation) much easier to solve than regular infix math.&lt;/p&gt;

&lt;p&gt;At first, I wrote a big if-else mess (you might’ve done that too 😅), but then I realized: why not use a simple approach that handles everything neatly using operator &lt;strong&gt;precedence&lt;/strong&gt;?&lt;/p&gt;

&lt;p&gt;Here’s the final version I settled on:&lt;br&gt;
&lt;/p&gt;

&lt;div class="highlight js-code-highlight"&gt;
&lt;pre class="highlight python"&gt;&lt;code&gt;&lt;span class="k"&gt;def&lt;/span&gt; &lt;span class="nf"&gt;infix_to_postfix&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;infix&lt;/span&gt;&lt;span class="p"&gt;):&lt;/span&gt;
    &lt;span class="n"&gt;postfix&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="p"&gt;[]&lt;/span&gt;
    &lt;span class="n"&gt;stack&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="p"&gt;[]&lt;/span&gt;
    &lt;span class="n"&gt;precedence&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="p"&gt;{&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;+&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="mi"&gt;1&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;-&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="mi"&gt;1&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;*&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="mi"&gt;2&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;/&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt; &lt;span class="mi"&gt;2&lt;/span&gt;&lt;span class="p"&gt;}&lt;/span&gt;
    &lt;span class="k"&gt;for&lt;/span&gt; &lt;span class="n"&gt;token&lt;/span&gt; &lt;span class="ow"&gt;in&lt;/span&gt; &lt;span class="n"&gt;infix&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
        &lt;span class="k"&gt;if&lt;/span&gt; &lt;span class="n"&gt;token&lt;/span&gt; &lt;span class="ow"&gt;not&lt;/span&gt; &lt;span class="ow"&gt;in&lt;/span&gt; &lt;span class="n"&gt;precedence&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
            &lt;span class="n"&gt;postfix&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;append&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;token&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
        &lt;span class="k"&gt;else&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
            &lt;span class="k"&gt;while&lt;/span&gt; &lt;span class="n"&gt;stack&lt;/span&gt; &lt;span class="ow"&gt;and&lt;/span&gt; &lt;span class="n"&gt;precedence&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;get&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="o"&gt;-&lt;/span&gt;&lt;span class="mi"&gt;1&lt;/span&gt;&lt;span class="p"&gt;],&lt;/span&gt; &lt;span class="mi"&gt;0&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt; &lt;span class="o"&gt;&amp;gt;=&lt;/span&gt; &lt;span class="n"&gt;precedence&lt;/span&gt;&lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="n"&gt;token&lt;/span&gt;&lt;span class="p"&gt;]:&lt;/span&gt;
                &lt;span class="n"&gt;postfix&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;append&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;pop&lt;/span&gt;&lt;span class="p"&gt;())&lt;/span&gt;
            &lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;append&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;token&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
    &lt;span class="k"&gt;while&lt;/span&gt; &lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
        &lt;span class="n"&gt;postfix&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;append&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;pop&lt;/span&gt;&lt;span class="p"&gt;())&lt;/span&gt;
    &lt;span class="nf"&gt;postfix_to_solution&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;postfix&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;

&lt;/div&gt;






&lt;h3&gt;
  
  
  But what’s really going on here?
&lt;/h3&gt;

&lt;ul&gt;
&lt;li&gt;&lt;p&gt;I created a &lt;code&gt;precedence&lt;/code&gt; dictionary to decide which operators are stronger (&lt;code&gt;*&lt;/code&gt; and &lt;code&gt;/&lt;/code&gt; are stronger than &lt;code&gt;+&lt;/code&gt; and &lt;code&gt;-&lt;/code&gt;).&lt;/p&gt;&lt;/li&gt;
&lt;li&gt;
&lt;p&gt;Then, I loop through each token in the infix list:&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;If it’s a number, it goes straight to the &lt;code&gt;postfix&lt;/code&gt; list.&lt;/li&gt;
&lt;li&gt;
&lt;p&gt;If it’s an operator, we compare it with the one on top of the stack:&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;If the stack's operator has &lt;strong&gt;higher or equal precedence&lt;/strong&gt;, we pop it out and add it to &lt;code&gt;postfix&lt;/code&gt;.&lt;/li&gt;
&lt;li&gt;Otherwise, we just push our current operator onto the stack.&lt;/li&gt;
&lt;/ul&gt;


&lt;/li&gt;

&lt;/ul&gt;

&lt;/li&gt;

&lt;li&gt;&lt;p&gt;Once we're done looping, we pop any remaining operators from the stack and add them to the result.&lt;/p&gt;&lt;/li&gt;

&lt;/ul&gt;




&lt;h3&gt;
  
  
  Example Time!
&lt;/h3&gt;

&lt;p&gt;Let’s say the infix expression is:&lt;br&gt;
&lt;/p&gt;

&lt;div class="highlight js-code-highlight"&gt;
&lt;pre class="highlight python"&gt;&lt;code&gt;&lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;12&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;+&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;7&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;*&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;5&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;]&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;

&lt;/div&gt;



&lt;p&gt;This function turns it into:&lt;br&gt;
&lt;/p&gt;

&lt;div class="highlight js-code-highlight"&gt;
&lt;pre class="highlight python"&gt;&lt;code&gt;&lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;12&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;7&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;5&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;*&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;+&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;]&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;

&lt;/div&gt;



&lt;h1&gt;
  
  
  3. Solve it
&lt;/h1&gt;

&lt;h2&gt;
  
  
  &lt;code&gt;postfix_to_solution(postfix)&lt;/code&gt;
&lt;/h2&gt;

&lt;p&gt;Alright, we’ve got our expression nicely converted into postfix form. Now it’s time for the grand finale — solving it! This function takes that postfix list and actually &lt;strong&gt;computes the answer&lt;/strong&gt;. Here's the code:&lt;br&gt;
&lt;/p&gt;

&lt;div class="highlight js-code-highlight"&gt;
&lt;pre class="highlight python"&gt;&lt;code&gt;&lt;span class="k"&gt;def&lt;/span&gt; &lt;span class="nf"&gt;postfix_to_solution&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;postfix&lt;/span&gt;&lt;span class="p"&gt;):&lt;/span&gt;
    &lt;span class="n"&gt;stack&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="p"&gt;[]&lt;/span&gt;
    &lt;span class="k"&gt;for&lt;/span&gt; &lt;span class="n"&gt;token&lt;/span&gt; &lt;span class="ow"&gt;in&lt;/span&gt; &lt;span class="n"&gt;postfix&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
        &lt;span class="k"&gt;if&lt;/span&gt; &lt;span class="n"&gt;token&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;isdigit&lt;/span&gt;&lt;span class="p"&gt;():&lt;/span&gt;
            &lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;append&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="nf"&gt;int&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;token&lt;/span&gt;&lt;span class="p"&gt;))&lt;/span&gt;
        &lt;span class="k"&gt;else&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
            &lt;span class="n"&gt;b&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;pop&lt;/span&gt;&lt;span class="p"&gt;()&lt;/span&gt;
            &lt;span class="n"&gt;a&lt;/span&gt; &lt;span class="o"&gt;=&lt;/span&gt; &lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;pop&lt;/span&gt;&lt;span class="p"&gt;()&lt;/span&gt;
            &lt;span class="k"&gt;if&lt;/span&gt; &lt;span class="n"&gt;token&lt;/span&gt; &lt;span class="o"&gt;==&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;+&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
                &lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;append&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;a&lt;/span&gt; &lt;span class="o"&gt;+&lt;/span&gt; &lt;span class="n"&gt;b&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
            &lt;span class="k"&gt;elif&lt;/span&gt; &lt;span class="n"&gt;token&lt;/span&gt; &lt;span class="o"&gt;==&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;-&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
                &lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;append&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;a&lt;/span&gt; &lt;span class="o"&gt;-&lt;/span&gt; &lt;span class="n"&gt;b&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
            &lt;span class="k"&gt;elif&lt;/span&gt; &lt;span class="n"&gt;token&lt;/span&gt; &lt;span class="o"&gt;==&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;*&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
                &lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;append&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;a&lt;/span&gt; &lt;span class="o"&gt;*&lt;/span&gt; &lt;span class="n"&gt;b&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
            &lt;span class="k"&gt;elif&lt;/span&gt; &lt;span class="n"&gt;token&lt;/span&gt; &lt;span class="o"&gt;==&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;/&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
                &lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;.&lt;/span&gt;&lt;span class="nf"&gt;append&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="n"&gt;a&lt;/span&gt; &lt;span class="o"&gt;/&lt;/span&gt; &lt;span class="n"&gt;b&lt;/span&gt;&lt;span class="p"&gt;)&lt;/span&gt;
    &lt;span class="k"&gt;if&lt;/span&gt; &lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;:&lt;/span&gt;
        &lt;span class="nf"&gt;print&lt;/span&gt;&lt;span class="p"&gt;(&lt;/span&gt;&lt;span class="sh"&gt;"&lt;/span&gt;&lt;span class="s"&gt;Result:&lt;/span&gt;&lt;span class="sh"&gt;"&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="n"&gt;stack&lt;/span&gt;&lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="mi"&gt;0&lt;/span&gt;&lt;span class="p"&gt;])&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;

&lt;/div&gt;






&lt;h3&gt;
  
  
  What’s happening here?
&lt;/h3&gt;

&lt;p&gt;This is a classic &lt;strong&gt;postfix evaluation using a stack&lt;/strong&gt;:&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;&lt;p&gt;If the token is a number, we push it onto the stack.&lt;/p&gt;&lt;/li&gt;
&lt;li&gt;
&lt;p&gt;If it’s an operator (&lt;code&gt;+&lt;/code&gt;, &lt;code&gt;-&lt;/code&gt;, &lt;code&gt;*&lt;/code&gt;, or &lt;code&gt;/&lt;/code&gt;), we pop &lt;strong&gt;two numbers&lt;/strong&gt; from the stack:&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;
&lt;code&gt;a&lt;/code&gt; and &lt;code&gt;b&lt;/code&gt;, where &lt;code&gt;a&lt;/code&gt; is the second-last and &lt;code&gt;b&lt;/code&gt; is the last one pushed.&lt;/li&gt;
&lt;/ul&gt;


&lt;/li&gt;

&lt;li&gt;&lt;p&gt;We perform the operation: &lt;code&gt;a + b&lt;/code&gt;, &lt;code&gt;a - b&lt;/code&gt;, etc., and push the result back onto the stack.&lt;/p&gt;&lt;/li&gt;

&lt;li&gt;&lt;p&gt;In the end, if everything went well, the stack will contain &lt;strong&gt;one final value&lt;/strong&gt; — the answer!&lt;/p&gt;&lt;/li&gt;

&lt;/ul&gt;




&lt;h3&gt;
  
  
  Example:
&lt;/h3&gt;

&lt;p&gt;Say your postfix list is:&lt;br&gt;
&lt;/p&gt;

&lt;div class="highlight js-code-highlight"&gt;
&lt;pre class="highlight python"&gt;&lt;code&gt;&lt;span class="p"&gt;[&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;12&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;7&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;5&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;*&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;,&lt;/span&gt; &lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="s"&gt;+&lt;/span&gt;&lt;span class="sh"&gt;'&lt;/span&gt;&lt;span class="p"&gt;]&lt;/span&gt;
&lt;/code&gt;&lt;/pre&gt;

&lt;/div&gt;



&lt;p&gt;Here's how the evaluation would go:&lt;/p&gt;

&lt;ol&gt;
&lt;li&gt;&lt;p&gt;Push &lt;code&gt;12&lt;/code&gt;&lt;/p&gt;&lt;/li&gt;
&lt;li&gt;&lt;p&gt;Push &lt;code&gt;7&lt;/code&gt;&lt;/p&gt;&lt;/li&gt;
&lt;li&gt;&lt;p&gt;Push &lt;code&gt;5&lt;/code&gt;&lt;/p&gt;&lt;/li&gt;
&lt;li&gt;&lt;p&gt;See &lt;code&gt;*&lt;/code&gt; → pop &lt;code&gt;5&lt;/code&gt; and &lt;code&gt;7&lt;/code&gt; → push &lt;code&gt;35&lt;/code&gt;&lt;/p&gt;&lt;/li&gt;
&lt;li&gt;&lt;p&gt;See &lt;code&gt;+&lt;/code&gt; → pop &lt;code&gt;35&lt;/code&gt; and &lt;code&gt;12&lt;/code&gt; → push &lt;code&gt;47&lt;/code&gt;&lt;/p&gt;&lt;/li&gt;
&lt;/ol&gt;

&lt;h2&gt;
  
  
  Final result: &lt;code&gt;47&lt;/code&gt;
&lt;/h2&gt;

&lt;h3&gt;
  
  
  Quick Note
&lt;/h3&gt;

&lt;h3&gt;
  
  
  This code uses &lt;code&gt;int()&lt;/code&gt; to convert digits, so it won’t work with decimal numbers like &lt;code&gt;2.5&lt;/code&gt; yet. If you want to support floats, just change &lt;code&gt;int(token)&lt;/code&gt; to &lt;code&gt;float(token)&lt;/code&gt; — easy fix!
&lt;/h3&gt;

&lt;p&gt;&lt;strong&gt;And that’s it…, now ask yourself.&lt;br&gt;&lt;br&gt;
“Is there any room of improvement?”&lt;/strong&gt;&lt;/p&gt;

&lt;p&gt;&lt;strong&gt;Yes! A lot!.&lt;/strong&gt;&lt;/p&gt;

&lt;p&gt;&lt;strong&gt;There’s also one major issue with this calculator. Try giving it an input like&lt;/strong&gt; &lt;code&gt;2++3-2&lt;/code&gt; &lt;strong&gt;— yeah, it breaks! 😅 It doesn’t currently handle invalid operator sequences properly. I’m leaving this part on you to fix.&lt;/strong&gt;&lt;/p&gt;

&lt;h2&gt;
  
  
  &lt;strong&gt;There are a lot of other things you can do with this, maybe try adding brackets support?.&lt;/strong&gt;
&lt;/h2&gt;

&lt;h2&gt;
  
  
  🎯 Wrapping it up
&lt;/h2&gt;

&lt;p&gt;This calculator may be simple, but building it helped me understand how real interpreters work behind the scenes. From reading input, validating it, converting between notations, and finally evaluating — it’s all there.&lt;/p&gt;

&lt;p&gt;There’s still room for improvements — like handling decimals, parentheses, or even making a GUI. But I’ll leave that challenge to you!&lt;/p&gt;

&lt;p&gt;Thanks for reading 😄&lt;br&gt;&lt;br&gt;
Let me know in the comments what you added or improved!&lt;/p&gt;

</description>
      <category>programming</category>
      <category>beginners</category>
      <category>tutorial</category>
      <category>python</category>
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