[GS] New: Python Hello World

_data/navigation.yml

@@ -34,3 +34,5 @@ getting_started_0:
         url: /categories/getting_started/programming_tutorial_I
       - title: "Programming Tutorial II"
         url: /categories/getting_started/programming_tutorial_II
+      - title: "Python: Hello World"
+        url: /categories/getting_started/python_hello_world

_posts/2025-07-26-gs_00010_python-hello-world.md

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+---
+layout: single
+title: "Python: Hello World"
+category: Getting Started
+permalink: /categories/getting_started/python_hello_world
+excerpt: "Your first Python Program"
+description:
+  In this blog post you will learn how to write your first Python program.
+author: Bjoern Hartmann
+toc: true
+toc_label: "Content"
+toc_sticky: true
+toc_icon: "align-justify"
+sidebar:
+  nav: "getting_started_0"
+header:
+  overlay_color: "#000"
+  overlay_filter: "0.5"
+  overlay_image: /assets/images/getting_started.jpeg
+---
+
+Welcome back to our next post where you'll finally learn how to write your first
+Python program. In our latest [post](/categories/getting_started/visual_code),
+we introduced VS Code, a modern and flexible IDE. The prepared profile, which we
+used to set up the editor, already includes extensions for the Python language.
+So, everything should be ready to get started. In another previous post about
+[programming concepts](/categories/getting_started/programming_tutorial_II), we
+learned about concepts, such as functions or loops, that all programming
+languages have in common. We will see how these simple structures are used in a
+working program.
+
+Python is one of the most beginner-friendly programming languages, known for its
+readability and simplicity. Therefore, it's a perfect starting point for us.
+Once you know how to use one language it's just a small step to learn another
+language. The core principles are always the same. In our first program, we'll
+implement the traditional "Hello, World!".
+
+## Hello World!
+
+A "Hello, World!" program is usually the first piece of code written when
+learning a new programming language. It does something very simple: It displays
+the message **Hello, World!**. While it may seem trivial, this program serves a
+very important purpose. First, it helps to verify that your development
+environment is set up correctly. If the program runs and outputs "Hello, World!"
+to your screen, you know that your interpreter, editor, and everything else are
+working as expected. Secondly, it introduces the basic syntax of the language.
+It shows how to output data to the console, which is a fundamental capability in
+programming. Lastly, it serves as a confidence booster. By successfully running
+your first program, you're building momentum for more complex projects.
+
+Inside VS Code, open a folder of your choice and create a new file
+_hello_world.py_. By the _.py_ extension, VS Code knows immediately that it is a
+Python file. In the lower-right corner, VS Code shows that it is in Python mode
+and it shows the current Python version (see the picture below). Just a quick
+note on Python versions: Each version introduces new features of the programming
+language. Usually, this is backward compatible. So, a program written for Python
+3.6 also works for our 3.13 version. This is not true for major releases. It's
+not possible to run a Python 2 program with Python 3.
+
+Now, write the following code and save it:
+
+```python
+    print("Hello World!")
+```
+
+The code is probably very easy to understand. _print_ is a Python function that
+can be used to print a message to the console. The message itself has to be
+within single or double quotes. To run the code you can hit the run button in
+the upper-right. This will open a terminal where your Python script is executed.
+If everything goes well you should see the _Hello World!_ output. Alternatively,
+you can directly run the program by typing _python hello_world.py_ into the
+console.
+
+Congrats! This was your very first Python program.
+
+<figure class="img-center" style="width:85%">
+  <img src="/assets/images/gs_00010_python_hello_world.png" title="Hello World" alt="Hello World">
+</figure>
+
+Note that the terminal probably looks different for you. We will cover this in a
+later post.
+
+## Python as Calculator
+
+In most cases, you will write all Python commands into a file and execute the
+file, as we did in our _Hello World!_ program. However, sometimes it is useful
+to execute the commands interactively. Inside the terminal, just type the
+command
+
+    $ python
+
+This will lead you to an input prompt where you can type your Python commands,
+for example, the _print("Hello World!")_ command from the previous section. You
+can also do calculations such as _3\*3_. This can be very handy. Just play
+around with it!
+
+<figure class="img-center" style="width:85%">
+  <img src="/assets/images/gs_00010_python_calculator.png" title="Python as calculator" alt="Python as calculator">
+</figure>
+
+## Let's Build a Counter
+
+Now that you’ve successfully written your first Python program, let’s build
+something a little more useful: a counter. This simple project will introduce us
+to more key concepts in Python, such as variables, loops, functions, and
+conditional statements.
+
+### Starting with a simple counter
+
+We can begin by writing a basic counter that prints numbers. Create a new file
+_counter.py_ and add the following code:
+
+```python
+count = 1
+print("Count is:", count)
+```
+
+In this case, we define a **variable** called _count_ and set it to 1. The
+_print()_ function is used to output the value of _count_ to the screen. Unlike
+printing a fixed message like "Hello World", notice that we don't put the
+variable name in quotes. Doing so would print the word "count" instead of its
+value.
+
+> Count is: 1
+
+### Adding a while Loop
+
+Next, let's use a **while loop** to make the counter print numbers from 1 to 5.
+A loop helps us automate repetitive tasks, so instead of manually printing each
+count, we can write a single block of code that runs until a condition is met.
+
+Here’s how we modify the counter to use a loop:
+
+```python
+count = 1
+while count <= 5:
+    print("Count is:", count)
+    count += 1
+```
+
+In this version, the variable _count_ starts at 1. The while loop checks whether
+_count_ is less than or equal to 5. As long as that condition is true, the loop
+keeps running. Inside the loop, the program prints the current value of _count_,
+then increases it by 1 using _count_ += 1. Once _count_ reaches 6, the condition
+becomes false, and the loop ends.
+
+An important detail here is **indentation**. Python uses indentation to show
+which lines of code belong to the loop. Any indented lines after the while
+statement are considered part of the loop and will be repeated each time it
+runs. Without the correct indentation, Python won’t know what to include in the
+loop and will raise an error.
+
+> Count is: 1<br> Count is: 2<br> Count is: 3<br> Count is: 4<br> Count is: 5
+
+### Encapsulating the Code in a Function
+
+Another useful concept in programming is the **function**. Functions allow you
+to group code to be reused in different parts of your program. Let’s put our
+counter logic into a function:
+
+```python
+def simple_counter(target):
+    count = 1
+    while count <= target:
+        print("Count is:", count)
+        count += 1
+
+simple_counter(5)
+```
+
+Functions are **defined** by the keyword _def_ followed by a function name.
+Here, we additionally add a **parameter** with the name _target_ to set the
+upper limit for our counter. Observe that the previous limit _5_ is replaced by
+the parameter. Also note that again indentation defines which commands belong to
+the function.
+
+At the end, you just have to **call** the function passing a value for the
+parameter. If you pass _5_, the output is exactly the same as with the previous
+code without function. Try to use different values and observe the output. Using
+functions has three major benefits:
+
+1. **Code organization**: It is easy to understand your code if it is structured
+   in small logical blocks.
+2. **Reusability**: If you need a second counter, you just need to call the
+   function again
+3. **Abstraction**: Functions can be very complex, but often it's not required
+   to know how they work. It is sufficient to know what they do and how you can
+   use them. Take the print() function as an example. We didn't explain how it
+   works, but you still can use it.
+
+### Conditional statements
+
+Next, we want to improve the text output using the following logic:
+
+- If the count has reached the target, print "finally done".
+- If the count is greater than or equal to the target minus 2, print "almost
+  there".
+- Otherwise, print "stay patient".
+
+We can use **if-else** statements to directly translate this logic into
+programming code:
+
+```python
+def simple_counter(target):
+    count = 1
+    while count <= target:
+        if count == target:
+            print("Finally done! Count is:", count)
+        elif count >= target - 2:
+            print("Almost there! Count is:", count)
+        else:
+            print("Stay patient! Count is:", count)
+        count += 1
+
+simple_counter(5)
+```
+
+**if** is used to check for a condition. Note that in case you want to check for
+equality, you have to use "==" and **not** "=". This is a common beginner
+mistake. The latter one is only used for assigning a value to a
+variable.**elif** (short for 'else if') is used to check a second condition if
+the if condition is false. You can include as many elif clauses as needed.
+**else** handles all remaining cases and acts as the "otherwise" in your
+program. Again, indentation shows which command belongs to which structure.
+
+> Stay patient! Count is: 1<br> Stay patient! Count is: 2<br> Almost there!
+> Count is: 3<br> Almost there! Count is: 4<br> Finally done! Count is: 5
+
+### Comments
+
+"What the \*\*\*\* have I done here?" - This is a question you will probably ask
+yourself very soon. Sometimes, code is complex and to be able to understand it
+in a few days (or years) later it is crucial to leave some comments. For
+functions, it is good practise to explain what they do in the first line. For
+other locations it depends. A general rule is to comment as little as possible
+but as much as necessary. There are three major ways of commenting in Python:
+
+```python
+def simple_counter(target):
+    """
+    Prints numbers from 1 up to the given target (inclusive).
+
+    This is a Docstring (multi-line comment),
+    which is often used for documenting functions
+    """
+    count = 1
+    while count <= target:
+        if count == target:
+            print("Finally done! Count is:", count)
+        elif count >= target - 2:
+            print("Almost there! Count is:", count)
+        else:
+            print("Stay patient! Count is:", count)
+        count += 1
+
+# I am a single-line comment
+simple_counter(5) # I am an inline comment
+```
+
+## Side Note: Indentation & Style Guides
+
+You've learned already that indentation is crucial for structuring your program.
+In Python, it plays an even more important role because it defines which
+commands belong to which blocks of code. However, we haven't yet defined what
+indentation actually is. The reason is that there’s no single standard and
+programmers often debate the best way to handle it. On the one hand, you can use
+**tabs**, which take up less space in a file but may look different depending on
+the editor or environment. On the other hand, you can use **spaces**. Typically,
+2 or 4 spaces are used. Spaces offer a consistent appearance across all tools.
+In this blog, we’ve chosen to use four spaces, as they provide a clear and
+easy-to-read structure for your code. No matter what you use, use it
+consistently!
+
+Beyond indentation, there are many other aspects of coding style. For example,
+notice that we use one empty line between the function definition and the
+function call. This raises more questions:
+
+- Where should I use empty lines?
+- What’s the ideal maximum line length?
+- How should variables be named?
+
+There are many practical aspects that people try to standardize in so-called
+**style guides**. For Python, the most popular style guide is
+[PEP 8](https://peps.python.org/pep-0008/). While following such guides isn’t
+mandatory, doing so helps you write clean, readable, and maintainable code.
+
+## Summary
+
+We hope you enjoyed writing your first Python program! Let's quickly recap what
+we covered:
+
+- _Hello World_ programs are used to test your environment
+- Python can be used with scripts or interactively, for example, as a handy
+  calculator
+- You implemented your first program using basic programming concepts:
+  - Printing to the console
+  - Variables
+  - Loops
+  - Functions
+  - Conditional statements (if-else)
+  - Comments
+- [PEP 8](https://peps.python.org/pep-0008/) is a popular style guide for
+  Python.
+
+In our next post, we’ll build on this foundation by exploring more core Python
+concepts. Until then, happy coding, and don't forget to follow us on
+[X](https://x.com/bitsandvolts).