Executing python in linux

2. Using Python on Unix platforms¶

2.1. Getting and installing the latest version of Python¶

2.1.1. On Linux¶

Python comes preinstalled on most Linux distributions, and is available as a package on all others. However there are certain features you might want to use that are not available on your distro’s package. You can easily compile the latest version of Python from source.

In the event that Python doesn’t come preinstalled and isn’t in the repositories as well, you can easily make packages for your own distro. Have a look at the following links:

for Debian users

for OpenSuse users

for Fedora users

for Slackware users

2.1.2. On FreeBSD and OpenBSD¶

FreeBSD users, to add the package use:

OpenBSD users, to add the package use:

For example i386 users get the 2.5.1 version of Python using:

2.1.3. On OpenSolaris¶

You can get Python from OpenCSW. Various versions of Python are available and can be installed with e.g. pkgutil -i python27 .

2.2. Building Python¶

If you want to compile CPython yourself, first thing you should do is get the source. You can download either the latest release’s source or just grab a fresh clone. (If you want to contribute patches, you will need a clone.)

The build process consists of the usual commands:

Configuration options and caveats for specific Unix platforms are extensively documented in the README.rst file in the root of the Python source tree.

make install can overwrite or masquerade the python3 binary. make altinstall is therefore recommended instead of make install since it only installs exec_prefix /bin/python version .

These are subject to difference depending on local installation conventions; prefix ( $ ) and exec_prefix ( $ ) are installation-dependent and should be interpreted as for GNU software; they may be the same.

For example, on most Linux systems, the default for both is /usr .

Recommended location of the interpreter.

prefix /lib/python version , exec_prefix /lib/python version

Recommended locations of the directories containing the standard modules.

prefix /include/python version , exec_prefix /include/python version

Recommended locations of the directories containing the include files needed for developing Python extensions and embedding the interpreter.

2.4. Miscellaneous¶

To easily use Python scripts on Unix, you need to make them executable, e.g. with

and put an appropriate Shebang line at the top of the script. A good choice is usually

which searches for the Python interpreter in the whole PATH . However, some Unices may not have the env command, so you may need to hardcode /usr/bin/python3 as the interpreter path.

To use shell commands in your Python scripts, look at the subprocess module.

2.5. Custom OpenSSL¶

To use your vendor’s OpenSSL configuration and system trust store, locate the directory with openssl.cnf file or symlink in /etc . On most distribution the file is either in /etc/ssl or /etc/pki/tls . The directory should also contain a cert.pem file and/or a certs directory.

Download, build, and install OpenSSL. Make sure you use install_sw and not install . The install_sw target does not override openssl.cnf .

Build Python with custom OpenSSL (see the configure —with-openssl and —with-openssl-rpath options)

Patch releases of OpenSSL have a backwards compatible ABI. You don’t need to recompile Python to update OpenSSL. It’s sufficient to replace the custom OpenSSL installation with a newer version.

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Запуск python скрипта в Linux

Python — очень популярный язык программирования для написания различных системных скриптов в Linux. В Windows, там где не хватает возможностей командной оболочки используется PowerShell. В Linux же, когда возможностей Bash не хватает используется язык Python.

На этом языке написано огромное количество системных программ, среди них пакетный менеджер apt, видеоредактор OpenShot, а также множество скриптов, которые вы можете установить с помощью утилиты pip. В этой небольшой статье мы рассмотрим как запустить Python скрипт в Linux с помощью терминала различными способами.

Запуск python скрипта в Linux

Для примера нам понадобится Python скрипт. Чтобы не брать какой-либо из существующих скриптов, давайте напишем свой:

print(«Hello from losst!»)

Для того чтобы запустить скрипт необходимо передать его интерпретатору Python. Для этого просто откройте терминал с помощью сочетания клавиш Ctrl + Alt + T, перейдите в папку со скриптом и выполните:

Если вы хотите, чтобы после выполнения скрипта открылась консоль, в которой можно интерактивно выполнять команды языка Python используйте опцию -i:

python -i script.py

Но как вы могли заметить, при запуске apt или openshot не надо писать слово python. Это намного удобнее. Давайте разберемся как это реализовать. Если вы не хотите указывать интерпретатор в командной строке, его надо указать в самом скрипте. Для этого следует в начало скрипта добавить такую строчку:

Сохраните изменения, а затем сделайте файл скрипта исполняемым с помощью такой команды:

chmod ugo+x script.py

После этого можно запустить скрипт Python просто обращаясь к его файлу:

Если убрать расширение .py и переместить скрипт в каталог, находящийся в переменной PATH, например /usr/bin/, то его можно будет выполнять вот так:

Как видите, запуск команды python Linux выполняется довольно просто и для этого даже есть несколько способов. А каким способом пользуетесь вы? Напишите в комментариях!

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2. Using the Python Interpreter¶

2.1. Invoking the Interpreter¶

The Python interpreter is usually installed as /usr/local/bin/python3.11 on those machines where it is available; putting /usr/local/bin in your Unix shell’s search path makes it possible to start it by typing the command:

to the shell. 1 Since the choice of the directory where the interpreter lives is an installation option, other places are possible; check with your local Python guru or system administrator. (E.g., /usr/local/python is a popular alternative location.)

On Windows machines where you have installed Python from the Microsoft Store , the python3.11 command will be available. If you have the py.exe launcher installed, you can use the py command. See Excursus: Setting environment variables for other ways to launch Python.

Typing an end-of-file character ( Control — D on Unix, Control — Z on Windows) at the primary prompt causes the interpreter to exit with a zero exit status. If that doesn’t work, you can exit the interpreter by typing the following command: quit() .

The interpreter’s line-editing features include interactive editing, history substitution and code completion on systems that support the GNU Readline library. Perhaps the quickest check to see whether command line editing is supported is typing Control — P to the first Python prompt you get. If it beeps, you have command line editing; see Appendix Interactive Input Editing and History Substitution for an introduction to the keys. If nothing appears to happen, or if ^P is echoed, command line editing isn’t available; you’ll only be able to use backspace to remove characters from the current line.

The interpreter operates somewhat like the Unix shell: when called with standard input connected to a tty device, it reads and executes commands interactively; when called with a file name argument or with a file as standard input, it reads and executes a script from that file.

A second way of starting the interpreter is python -c command [arg] . , which executes the statement(s) in command, analogous to the shell’s -c option. Since Python statements often contain spaces or other characters that are special to the shell, it is usually advised to quote command in its entirety.

Some Python modules are also useful as scripts. These can be invoked using python -m module [arg] . , which executes the source file for module as if you had spelled out its full name on the command line.

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When a script file is used, it is sometimes useful to be able to run the script and enter interactive mode afterwards. This can be done by passing -i before the script.

All command line options are described in Command line and environment .

2.1.1. Argument Passing¶

When known to the interpreter, the script name and additional arguments thereafter are turned into a list of strings and assigned to the argv variable in the sys module. You can access this list by executing import sys . The length of the list is at least one; when no script and no arguments are given, sys.argv[0] is an empty string. When the script name is given as ‘-‘ (meaning standard input), sys.argv[0] is set to ‘-‘ . When -c command is used, sys.argv[0] is set to ‘-c’ . When -m module is used, sys.argv[0] is set to the full name of the located module. Options found after -c command or -m module are not consumed by the Python interpreter’s option processing but left in sys.argv for the command or module to handle.

2.1.2. Interactive Mode¶

When commands are read from a tty, the interpreter is said to be in interactive mode. In this mode it prompts for the next command with the primary prompt, usually three greater-than signs ( >>> ); for continuation lines it prompts with the secondary prompt, by default three dots ( . ). The interpreter prints a welcome message stating its version number and a copyright notice before printing the first prompt:

Continuation lines are needed when entering a multi-line construct. As an example, take a look at this if statement:

For more on interactive mode, see Interactive Mode .

2.2. The Interpreter and Its Environment¶

2.2.1. Source Code Encoding¶

By default, Python source files are treated as encoded in UTF-8. In that encoding, characters of most languages in the world can be used simultaneously in string literals, identifiers and comments — although the standard library only uses ASCII characters for identifiers, a convention that any portable code should follow. To display all these characters properly, your editor must recognize that the file is UTF-8, and it must use a font that supports all the characters in the file.

To declare an encoding other than the default one, a special comment line should be added as the first line of the file. The syntax is as follows:

where encoding is one of the valid codecs supported by Python.

For example, to declare that Windows-1252 encoding is to be used, the first line of your source code file should be:

One exception to the first line rule is when the source code starts with a UNIX “shebang” line . In this case, the encoding declaration should be added as the second line of the file. For example:

On Unix, the Python 3.x interpreter is by default not installed with the executable named python , so that it does not conflict with a simultaneously installed Python 2.x executable.

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How to Run Your Python Scripts

Table of Contents

Watch Now This tutorial has a related video course created by the Real Python team. Watch it together with the written tutorial to deepen your understanding: Running Python Scripts

One of the most important skills you need to build as a Python developer is to be able to run Python scripts and code. This is going to be the only way for you to know if your code works as you planned. It’s even the only way of knowing if your code works at all!

This step-by-step tutorial will guide you through a series of ways to run Python scripts, depending on your environment, platform, needs, and skills as a programmer.

You’ll have the opportunity to learn how to run Python scripts by using:

  • The operating system command-line or terminal
  • The Python interactive mode
  • The IDE or text editor you like best
  • The file manager of your system, by double-clicking on the icon of your script

This way, you’ll get the knowledge and skills you’ll need to make your development cycle more productive and flexible.

Free Download: Get a sample chapter from Python Tricks: The Book that shows you Python’s best practices with simple examples you can apply instantly to write more beautiful + Pythonic code.

Take the Quiz: Test your knowledge with our interactive “How to Run Your Python Scripts” quiz. Upon completion you will receive a score so you can track your learning progress over time:

Scripts vs Modules

In computing, the word script is used to refer to a file containing a logical sequence of orders or a batch processing file. This is usually a simple program, stored in a plain text file.

Scripts are always processed by some kind of interpreter, which is responsible for executing each command sequentially.

A plain text file containing Python code that is intended to be directly executed by the user is usually called script, which is an informal term that means top-level program file.

On the other hand, a plain text file, which contains Python code that is designed to be imported and used from another Python file, is called module.

So, the main difference between a module and a script is that modules are meant to be imported, while scripts are made to be directly executed.

In either case, the important thing is to know how to run the Python code you write into your modules and scripts.

What’s the Python Interpreter?

Python is an excellent programming language that allows you to be productive in a wide variety of fields.

Python is also a piece of software called an interpreter. The interpreter is the program you’ll need to run Python code and scripts. Technically, the interpreter is a layer of software that works between your program and your computer hardware to get your code running.

Depending on the Python implementation you use, the interpreter can be:

  • A program written in C, like CPython, which is the core implementation of the language
  • A program written in Java, like Jython
  • A program written in Python itself, like PyPy
  • A program implemented in .NET, like IronPython

Whatever form the interpreter takes, the code you write will always be run by this program. Therefore, the first condition to be able to run Python scripts is to have the interpreter correctly installed on your system.

The interpreter is able to run Python code in two different ways:

  • As a script or module
  • As a piece of code typed into an interactive session

How to Run Python Code Interactively

A widely used way to run Python code is through an interactive session. To start a Python interactive session, just open a command-line or terminal and then type in python , or python3 depending on your Python installation, and then hit Enter .

Here’s an example of how to do this on Linux:

The standard prompt for the interactive mode is >>> , so as soon as you see these characters, you’ll know you are in.

Now, you can write and run Python code as you wish, with the only drawback being that when you close the session, your code will be gone.

When you work interactively, every expression and statement you type in is evaluated and executed immediately:

An interactive session will allow you to test every piece of code you write, which makes it an awesome development tool and an excellent place to experiment with the language and test Python code on the fly.

To exit interactive mode, you can use one of the following options:

  • quit() or exit() , which are built-in functions
  • The Ctrl + Z and Enter key combination on Windows, or just Ctrl + D on Unix-like systems

Note: The first rule of thumb to remember when using Python is that if you’re in doubt about what a piece of Python code does, then launch an interactive session and try it out to see what happens.

If you’ve never worked with the command-line or terminal, then you can try this:

On Windows, the command-line is usually known as command prompt or MS-DOS console, and it is a program called cmd.exe . The path to this program can vary significantly from one system version to another.

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A quick way to get access to it is by pressing the Win + R key combination, which will take you to the Run dialog. Once you’re there, type in cmd and press Enter .

On GNU/Linux (and other Unixes), there are several applications that give you access to the system command-line. Some of the most popular are xterm, Gnome Terminal, and Konsole. These are tools that run a shell or terminal like Bash, ksh, csh, and so on.

In this case, the path to these applications is much more varied and depends on the distribution and even on the desktop environment you use. So, you’ll need to read your system documentation.

On Mac OS X, you can access the system terminal from Applications → Utilities → Terminal.

How Does the Interpreter Run Python Scripts?

When you try to run Python scripts, a multi-step process begins. In this process the interpreter will:

Process the statements of your script in a sequential fashion

Compile the source code to an intermediate format known as bytecode

This bytecode is a translation of the code into a lower-level language that’s platform-independent. Its purpose is to optimize code execution. So, the next time the interpreter runs your code, it’ll bypass this compilation step.

Strictly speaking, this code optimization is only for modules (imported files), not for executable scripts.

Ship off the code for execution

At this point, something known as a Python Virtual Machine (PVM) comes into action. The PVM is the runtime engine of Python. It is a cycle that iterates over the instructions of your bytecode to run them one by one.

The PVM is not an isolated component of Python. It’s just part of the Python system you’ve installed on your machine. Technically, the PVM is the last step of what is called the Python interpreter.

The whole process to run Python scripts is known as the Python Execution Model.

Note: This description of the Python Execution Model corresponds to the core implementation of the language, that is, CPython. As this is not a language requirement, it may be subject to future changes.

How to Run Python Scripts Using the Command-Line

A Python interactive session will allow you to write a lot of lines of code, but once you close the session, you lose everything you’ve written. That’s why the usual way of writing Python programs is by using plain text files. By convention, those files will use the .py extension. (On Windows systems the extension can also be .pyw .)

Python code files can be created with any plain text editor. If you are new to Python programming, you can try Sublime Text, which is a powerful and easy-to-use editor, but you can use any editor you like.

To keep moving forward in this tutorial, you’ll need to create a test script. Open your favorite text editor and write the following code:

Save the file in your working directory with the name hello.py . With the test script ready, you can continue reading.

Using the python Command

To run Python scripts with the python command, you need to open a command-line and type in the word python , or python3 if you have both versions, followed by the path to your script, just like this:

If everything works okay, after you press Enter , you’ll see the phrase Hello World! on your screen. That’s it! You’ve just run your first Python script!

If this doesn’t work right, maybe you’ll need to check your system PATH , your Python installation, the way you created the hello.py script, the place where you saved it, and so on.

This is the most basic and practical way to run Python scripts.

Redirecting the Output

Sometimes it’s useful to save the output of a script for later analysis. Here’s how you can do that:

This operation redirects the output of your script to output.txt , rather than to the standard system output ( stdout ). The process is commonly known as stream redirection and is available on both Windows and Unix-like systems.

If output.txt doesn’t exist, then it’s automatically created. On the other hand, if the file already exists, then its contents will be replaced with the new output.

Finally, if you want to add the output of consecutive executions to the end of output.txt , then you must use two angle brackets ( >> ) instead of one, just like this:

Now, the output will be appended to the end of output.txt .

Running Modules With the -m Option

Python offers a series of command-line options that you can use according to your needs. For example, if you want to run a Python module, you can use the command python -m .

The -m option searches sys.path for the module name and runs its content as __main__ :

Note: module-name needs to be the name of a module object, not a string.

Using the Script Filename

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:

  • #!/usr/bin/python : writing the absolute path
  • #!/usr/bin/env python : using the operating system env command, which locates and executes Python by searching the PATH environment variable

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.

Finally, you need to note that if your script isn’t located at your current working directory, you’ll have to use the file path for this method to work correctly.

How to Run Python Scripts Interactively

It is also possible to run Python scripts and modules from an interactive session. This option offers you a variety of possibilities.

Taking Advantage of import

When you import a module, what really happens is that you load its contents for later access and use. The interesting thing about this process is that import runs the code as its final step.

When the module contains only classes, functions, variables, and constants definitions, you probably won’t be aware that the code was actually run, but when the module includes calls to functions, methods, or other statements that generate visible results, then you’ll witness its execution.

This provides you with another option to run Python scripts:

You’ll have to note that this option works only once per session. After the first import , successive import executions do nothing, even if you modify the content of the module. This is because import operations are expensive and therefore run only once. Here’s an example:

These two import operations do nothing, because Python knows that hello has already been imported.

There are some requirements for this method to work:

  • The file with the Python code must be located in your current working directory.
  • The file must be in the Python Module Search Path (PMSP), where Python looks for the modules and packages you import.

To know what’s in your current PMSP, you can run the following code:

Running this code, you’ll get the list of directories and .zip files where Python searches the modules you import.

Using importlib and imp

In the Python Standard Library, you can find importlib , which is a module that provides import_module() .

With import_module() , you can emulate an import operation and, therefore, execute any module or script. Take a look at this example:

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Once you’ve imported a module for the first time, you won’t be able to continue using import to run it. In this case, you can use importlib.reload() , which will force the interpreter to re-import the module again, just like in the following code:

An important point to note here is that the argument of reload() has to be the name of a module object, not a string:

If you use a string as an argument, then reload() will raise a TypeError exception.

Note: The output of the previous code has been abbreviated ( . ) in order to save space.

importlib.reload() comes in handy when you are modifying a module and want to test if your changes work, without leaving the current interactive session.

Finally, if you are using Python 2.x, then you’ll have imp , which is a module that provides a function called reload() . imp.reload() works similarly to importlib.reload() . Here’s an example:

In Python 2.x, reload() is a built-in function. In versions 2.6 and 2.7, it is also included in imp , to aid the transition to 3.x.

Note: imp has been deprecated since version 3.4 of the language. The imp package is pending deprecation in favor of importlib .

Using runpy.run_module() and runpy.run_path()

The Standard Library includes a module called runpy . In this module, you can find run_module() , which is a function that allows you to run modules without importing them first. This function returns the globals dictionary of the executed module.

Here’s an example of how you can use it:

The module is located using a standard import mechanism and then executed on a fresh module namespace.

The first argument of run_module() must be a string with the absolute name of the module (without the .py extension).

On the other hand, runpy also provides run_path() , which will allow you to run a module by providing its location in the filesystem:

Like run_module() , run_path() returns the globals dictionary of the executed module.

The path_name parameter must be a string and can refer to the following:

  • The location of a Python source file
  • The location of a compiled bytecode file
  • The value of a valid entry in the sys.path , containing a __main__ module ( __main__.py file)

Hacking exec()

So far, you’ve seen the most commonly used ways to run Python scripts. In this section, you’ll see how to do that by using exec() , which is a built-in function that supports the dynamic execution of Python code.

exec() provides an alternative way for running your scripts:

This statement opens hello.py , reads its content, and sends it to exec() , which finally runs the code.

The above example is a little bit out there. It’s just a “hack” that shows you how versatile and flexible Python can be.

Using execfile() (Python 2.x Only)

If you prefer to use Python 2.x, you can use a built-in function called execfile() , which is able to run Python scripts.

The first argument of execfile() has to be a string containing the path to the file you want to run. Here’s an example:

Here, hello.py is parsed and evaluated as a sequence of Python statements.

How to Run Python Scripts From an IDE or a Text Editor

When developing larger and more complex applications, it is recommended that you use an integrated development environment (IDE) or an advanced text editor.

Most of these programs offer the possibility of running your scripts from inside the environment itself. It is common for them to include a Run or Build command, which is usually available from the tool bar or from the main menu.

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.

Advanced text editors like Sublime Text and Visual Studio Code also allow you to run your scripts.

To grasp the details of how to run Python scripts from your preferred IDE or editor, you can take a look at its documentation.

How to Run Python Scripts From a File Manager

Running a script by double-clicking on its icon in a file manager is another possible way to run your Python scripts. This option may not be widely used in the development stage, but it may be used when you release your code for production.

In order to be able to run your scripts with a double-click, you must satisfy some conditions that will depend on your operating system.

Windows, for example, associates the extensions .py and .pyw with the programs python.exe and pythonw.exe respectively. This allows you to run your scripts by double-clicking on them.

When you have a script with a command-line interface, it is likely that you only see the flash of a black window on your screen. To avoid this annoying situation, you can add a statement like input(‘Press Enter to Continue. ‘) at the end of the script. This way, the program will stop until you press Enter .

This trick has its drawbacks, though. For example, if your script has any error, the execution will be aborted before reaching the input() statement, and you still won’t be able to see the result.

On Unix-like systems, you’ll probably be able to run your scripts by double-clicking on them in your file manager. To achieve this, your script must have execution permissions, and you’ll need to use the shebang trick you’ve already seen. Likewise, you may not see any results on screen when it comes to command-line interface scripts.

Because the execution of scripts through double-click has several limitations and depends on many factors (such as the operating system, the file manager, execution permissions, file associations), it is recommended that you see it as a viable option for scripts already debugged and ready to go into production.

Conclusion

With the reading of this tutorial, you have acquired the knowledge and skills you need to be able to run Python scripts and code in several ways and in a variety of situations and development environments.

You are now able to run Python scripts from:

  • The operating system command-line or terminal
  • The Python interactive mode
  • The IDE or text editor you like best
  • The file manager of your system, by double-clicking on the icon of your script

These skills will make your development process much faster, as well as more productive and flexible.

Take the Quiz: Test your knowledge with our interactive “How to Run Your Python Scripts” quiz. Upon completion you will receive a score so you can track your learning progress over time:

Watch Now This tutorial has a related video course created by the Real Python team. Watch it together with the written tutorial to deepen your understanding: Running Python Scripts

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About Leodanis Pozo Ramos

Leodanis is an industrial engineer who loves Python and software development. He’s a self-taught Python developer with 6+ years of experience. He’s an avid technical writer with a growing number of articles published on Real Python and other sites.

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