Which program to run python?

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In computing, the code is a language converted from a human language into a set of ‘words’ that the computer can understand. It is also referred to as a piece of statements together that forms a program. A simple function or a statement can also be considered a code.

On the other hand, a script is a file consisting of a logical sequence of instructions or a batch-processing file that is interpreted by another program instead of the computer processor.

In simple terms, a script is a simple program stored in plain file text which contains Python code. The user can directly execute the code. A script is also called a top-level program file.

A module is a Python object with random attributes you can bind and reference.

Basically, all scripting languages are considered to be programming languages. The main difference between the two is that programming languages are compiled, whereas scripting languages are interpreted.

Scripting languages are slower than programming languages and usually sit behind them. Since they only run on a programming language subset, they have less access to a computer’s local abilities.

Python can be called a scripting language as well as a programming language since it works both as a compiler and an interpreter. Standard Python can compile Python code into bytecodes and then interpret it just like Java and C.

However, considering the historical relationship between the general-purpose programming language and the scripting language, it would be more appropriate to say that Python is a general-purpose programming language that works nicely as a scripting language too.

The interpreter is a layer of software that works as a bridge between the program and the system hardware to keep the code running. A Python interpreter is an application that is responsible for running Python scripts.

The Python Interpreter works on the Read-Eval-Print-Loop (REPL) environment.

The interpreter terminates when we use the exit() or quit() command otherwise the execution keeps on going.

A Python Interpreter runs code in two ways:

The simplest way to start the interpreter is to open the terminal and then use the interpreter from the command line.

To open the command-line interpreter:

Running Python code through an interactive session is an extensively used way. An interactive session is an excellent development tool to venture with the language and allows you to test every piece of Python code on the go.

To initiate a Python interactive session, type python in the command line or terminal and hit the ENTER key from the keyboard.

An example of how to do this on Windows:

The >>> on the terminal represents the standard prompt for the interactive mode. You need to re-install Python on your system if you do not see these characters.

The statements you write when working with an interactive session are evaluated and executed immediately:

The only disadvantage is when you close the interactive session, the code no longer exists.

The term Python Execution Model is given to the entire multi-step process of running Python script.

The most sought-after way to write a Python program is using a plain text editor. The code written in the Python interactive session is lost once it is closed, though it allows the user to write many lines of code. On Windows, the files use the .py extension.

If you are at the beginning of working with Python, you can use editors like Sublime or Notepad++ which are easy to use, or any other text editors.

Now you need to create a test script. In order to do that, open your most-suited text editor and write the following code:

Then save the file on your desktop with the name first_script.py or anything you like. Remember you need to give the .py extension only.

The most basic and easy way to run a Python script is by using the python command. You need to open a command line and type the word python followed by the path to your script file like this:

Then you hit the ENTER button from the keyboard, and that's it. You can see the phrase Hello World! on the screen. Congrats! You just ran your first Python script.

However, if you do not get the output, you might want to check your system PATH and the place where you saved your file. If it still doesn’t work, re-install Python in your system and try again.

Windows and Unix-like systems have a process called stream redirection. You can redirect the output of your stream to some other file format instead of the standard system output. It is useful to save the output in a different file for later analysis.

An example of how you can do this:

What happens is your Python script is redirected to the output.txt file. If the file doesn’t exist, it is systematically created. However, if it already exists, the contents are replaced.

A module is a file that contains the Python code. It allows you to arrange your Python code in a logical manner. It defines functions, classes, and variables and can also include runnable code.

If you want to run a Python module, there are a lot of command-line options which Python offers according to the needs of the user. One of which is the command

It searches the module name in the sys.path and runs the content as

Note that the module-name is a module object and not any string.

Windows makes use of the system registers and file association to run Python scripts. It determines the program needed to run that particular file. You need to simply enter the file name containing the code.

An example of how to do this using the command prompt:

On GNU/Linux systems, you need to add a line before the text— #!/usr/bin/env python. Python considers this line nothing but the operating system considers it everything. It helps the system decide what program should it use to run the file.

The character combination #!, known as hashbang or shebang is what the line starts with, which is then followed by the interpreter path.

Finally, to run scripts, assign execution permissions and configure the hashbang line and then simply type the filename in the command line:

However, if it doesn’t work, you might want to check whether the script is located in your current working directory. Otherwise, you can use the path of the file for this method.

As we have discussed earlier, running Python scripts in an interactive session is the most common way of writing scripts and offers a wide range of possibilities.

Importing a module means loading its contents so that they can be later accessed and used. It is the most usual way of invoking the import machinery. It is analogous to #include in C or C++. Using import, the Python code in one module gets access to the code in another module.

An implementation of the import:

You can see its execution only when the module contains calls to functions, methods, or other statements which generate visible output.

One important thing to note is that the import option works only once per session. This is because these operations are expensive.

For this method to work efficiently, you should keep the file containing the Python code in your current working directory, and also the file should be in the Python Module Search Path (PMSP). The PMSP is the place where the modules and packages are imported.

You can run the code below to know what’s in your current PSMP:

You’ll get the list of directories and .zip files where your modules and packages are imported.

importlib is a module that is an implementation of the import statement in Python code. It contains the import_module whose work is to execute any module or script by imitating the import operation.

An example of performing this:

importlib.reload() is used to re-import the module since you cannot use import to run it for the second time. Even if you use import after the first time, it will do nothing. importlib.reload() is useful when you want to modify and test your changes without exiting the current session.

The following code shows that:

However, you can only use a module object and not any string as the argument of reload(). If you use a string as an argument, it will show a TypeError as follows:

The Python Standard Library has a module named runpy. run_module() is a function in runpy whose work is to execute modules without importing them in the first place.

The module is located using import and then executed. The first argument of the run_module() must contain a string:

Similarly, runpy contains another function run_path() which allows you to run a module by providing a location.

An example of such is as follows:

Both the functions return the globals dictionary of the executed module.

Other than the most commonly used ways to run Python script, there are other alternative ways. One such way is by using the built-in function exec(). It is used for the dynamic execution of Python code, be it a string or an object code.

An example of exec() is:

py_compile is a module that behaves like the import statement. It generates two functions— one to generate the bytecode from the source file and another when the source file is invoked as a script.

You can compile your Python script using this module:

The py_compile generates a new subdirectory named "__pycache__" if it doesn’t already exist. Inside the subdirectory, a Compiled Python File (.pyc) version of the script file is created. When you open the .pyc file, you can see the output of your Python script.

An Integrated Development Environment (IDE) is an application that allows a developer to build software within an integrated environment in addition to the required tools.

You can use the Python IDLE, a default IDE of the standard Python Distribution to write, debug, modify, and run your modules and scripts. You can use other IDEs like Spyder, PyCharm, Eclipse, and Jupyter Notebook, allowing you to run your scripts inside its environment.

You can also use popular text editors like Sublime and Atom to run Python scripts.

To run a Python script from your IDE or text editor, you must create a project first. Once it is created, add your .py file to it, or you can just simply create one using the IDE. Finally, run it, and you can see the output on your screen.

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If you want to run your Python script in a file manager, all you need to do is just double-click on the file icon. This option is mainly used in the production stage after you have released the source code.

However, to achieve this, some conditions must be met:

If you are using the command line for running your script, you might likely come through a situation where you’ll see a flash of a black window on the screen. To avert this, include a statement at the tail of the script — input(‘Enter’). This will exit the program only when you hit the ENTER key. Note that the input() function will work only if your code is free of errors.

Though it is easy to execute a script by just double-clicking on the file, it isn’t considered a feasible option because of the limitations and dependency factors it comes with, like the operating system, the file manager, execution permissions, and also file associations.

So it is suggested to use this option only after the code is debugged and ready to be in the production market.

Python's standard distribution includes IDLE as the default IDE, and you can use it to write, debug, modify, and run your modules and scripts. Other IDEs such as Eclipse-PyDev, PyCharm, Eric, and NetBeans also allow you to run Python scripts from inside the environment.

Even though most of today's Linux and Mac have Python pre-installed in it, the version might be out-of-date. So, it is always a good idea to install the most current version.

The easiest way to run Python is by using Thonny IDE.

The Thonny IDE comes with the latest version of Python bundled in it. So you don't have to install Python separately.

Follow the following steps to run Python on your computer.

If you don't want to use Thonny, here's how you can install and run Python on your computer.

Once you finish the installation process, you can run Python.

Once Python is installed, typing python in the command line will invoke the interpreter in immediate mode. We can directly type in Python code, and press Enter to get the output.

Try typing in 1 + 1 and press enter. We get 2 as the output. This prompt can be used as a calculator. To exit this mode, type quit() and press enter.

We can use any text editing software to write a Python script file.

We just need to save it with the .py extension. But using an IDE can make our life a lot easier. IDE is a piece of software that provides useful features like code hinting, syntax highlighting and checking, file explorers, etc. to the programmer for application development.

By the way, when you install Python, an IDE named IDLE is also installed. You can use it to run Python on your computer. It's a decent IDE for beginners.

When you open IDLE, an interactive Python Shell is opened.

Now you can create a new file and save it with .py extension. For example, hello.py

Write Python code in the file and save it. To run the file, go to Run > Run Module or simply click F5.

Now that we have Python up and running, we can write our first Python program.

Let's create a very simple program called Hello World. A "Hello, World!" is a simple program that outputs Hello, World! on the screen. Since it's a very simple program, it's often used to introduce a new programming language to beginners.

Type the following code in any text editor or an IDE and save it as hello_world.py

Then, run the file. You will get the following output.

Congratulations! You just wrote your first program in Python.

On recent versions of Windows, it is possible to run Python scripts by simply entering the name of the file containing the code at the command prompt:

This is possible because Windows uses the system registry and the file association to determine which program to use for running a particular file.

On Unix-like systems, such as GNU/Linux, you can achieve something similar. You’ll only have to add a first line with the text #!/usr/bin/env python, just as you did with hello.py.

For Python, this is a simple comment, but for the operating system, this line indicates what program must be used to run the file.

This line begins with the #! character combination, which is commonly called hash bang or shebang, and continues with the path to the interpreter.

There are two ways to specify the path to the interpreter:

This last option is useful if you bear in mind that not all Unix-like systems locate the interpreter in the same place.

Finally, to execute a script like this one, you need to assign execution permissions to it and then type in the filename at the command-line.

Here’s an example of how to do this:

With execution permissions and the shebang line properly configured, you can run the script by simply typing its filename at the command-line.