Introduction to Python syntax

Python Syntax

Syntax refers to a set of rules that governs the structure of a programming language.

set of rules defining the structure of a programming language

https://en.wikipedia.org/wiki/Syntax_(programming_languages)

First Python Program

Let’s write our first Python program, that prints “Hello, World” to the console. We’ll cover how to run Python in two different modes.

Interactive mode

Introduction to Python Interactive Shell

The Python interactive shell, also known as the Python REPL (Read-Eval-Print Loop), allows you to execute Python code in real-time. It is a very powerful way to test out new ideas or inspect modules and packages (remember help(x)).

Here’s the step to follow before using Python interactive shell:

1. Open a Terminal or CMD

On Windows, you can search for cmd and powershell
On macOS or Linux, open the Terminal application.

2. Start Python:

You should see a prompt that looks like this:

Python 3.x.x (default, ... )
[GCC ...] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

Using the interactive shell

Python 3.x.x (default, ... )
[GCC ...] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>
>>>"Hello, World"
Hello, World
>>>
>>>

Now you have written your first Python program.

To exit Python, you can enter exit(), quit(), or select Ctrl-Z.

Script mode

Python is usually run in script mode. This is a common way to run Python programs, especially for larger projects or when you want to execute a series of commands at once.

Steps to run Python in script mode

1. Create Python script:

Use a text editor or an Integrated Development Environment (IDE) to write your Python code.
Save the file with a .py extension. For example, you might create a file named script.py.

2. Open a Terminal or Command Prompt:

On Windows, you can use Command Prompt or PowerShell.
On macOS or Linux, open the Terminal application.

3. Navigate to the Directory:

Use the cd command to change to the directory where your Python script is located. For example:

  cd path/to/your/script

4. Run the Script:

Use the python or python3 command followed by the name of your script to run it. For example:

  python greeting.py

  python3 greeting.py

The output of the script will be displayed in the terminal. For the example above, you would see:

  Hello, Alice!

Indentation

Python uses whitespace indentation, rather than curly brackets {} to define the scope of blocks of code. Indentation in Python can be used to group related statements together. Curly braces can be used to create functions, control statements, and classes.

In simple Term

It’s a space added at the beginning of a code line. Identifying a block of code

The recommended indent size is four spaces.

Comments

Comments are ignored by the Python interpreter, meaning they do not affect the execution of the program. Everything after hash # character is ignored by the interpreter

  # This is comment
  x = 10
  print(x) # output: 10