One place for hosting & domains

      Python

      How to Use the Shebang in Bash and Python


      A
      Shebang directive, which always begins with the sequence #!, can sometimes be found on the first line of a Bash or Python script. In a Linux environment, the Shebang functions as an interpreter directive. This guide explains what a Shebang is and what advantages it provides. It also describes how to use a Shebang inside a Bash or Python script.

      What is a Shebang?

      The Shebang #! symbol indicates the interpreter, or which version of an interpreter, to use when executing a script. It is also known as the “sharp-exclamation”, “sha-bang”, “hash-bang”, or “pound-bang”. The name is believed to have originated as a partial contraction of either “SHarp bang” or “haSH bang”.

      A Shebang is always the first line of a script. Because it begins with the # symbol, the interpreter does not process the line containing the Shebang. When a Linux system executes a text file, it treats the Shebang as an interpreter directive. It locates the correct interpreter and runs it, passing the name of the file to the interpreter as input. For example, executing a file named ~/scripts/shebang that begins with the Shebang #!/bin/sh is functionally equivalent to running the command /bin/sh ~/scripts/shebang. The text file must be executable for proper processing to occur.

      The Shebang directive has the following advantages:

      • Permits users to treat scripts and files as commands.
      • Hides certain implementation details from users, such as the name of the interpreter.
      • Does not require the user to know the absolute path to the interpreter or how to use the env command.
      • Allows a particular version of an interpreter to be used, for example, python2 versus python3.
      • Allows the interpreter to be changed while maintaining the same user behavior and command.
      • Can automatically pass mandatory options through to the interpreter.

      One potential drawback can occur if the path to the interpreter is hard coded. If the location of the interpreter changes, the Shebang directive must be updated at the same time. Otherwise, the script might stop working.

      The Shebang directive follows this format.

      1
      
      #!interpreter [options]

      Here is an actual example of a Shebang instruction. This Shebang mandates the use of the sh Bourne shell to run the script. This example uses an absolute path to define the interpreter.

      The env utility can help find the path to the interpreter. In this case, the Shebang instructs the system to use /usr/bin/env to discover the path to the python2 interpreter. This technique is more robust because it continues to work if the path changes.

      To effectively implement a Shebang, keep in mind the following rules.

      • The directive must always begin with the #! character combination.
      • To work properly, a Shebang must occur on the first line of the file. If it is found in any other place, it is treated as a comment.
      • Either specify the full absolute path to the interpreter or use env to find the correct path.
      • Place any interpreter options after the name of the interpreter. Implementation details for compiler options vary between different systems. However, all major operating systems support at least one option.
      • One or more spaces between the #! character combo and the name of the interpreter are allowed, but not required. For example, the directives #!interpreter and #! interpreter are both valid and functionally equivalent.
      • Linux permits a second script to serve as the interpreter for the first script, but this is not the case for all operating systems.

      The directive #!/bin/false is a special Shebang. It immediately exits and returns a failure status. It prevents certain system files from being executed outside of their correct context.

      Before You Begin

      1. If you have not already done so, create a Linode account and Compute Instance. See our
        Getting Started with Linode and
        Creating a Compute Instance guides.

      2. Follow our
        Setting Up and Securing a Compute Instance guide to update your system. You may also wish to set the timezone, configure your hostname, create a limited user account, and harden SSH access.

      Note

      This guide is written for a non-root user. Commands that require elevated privileges are prefixed with sudo. If you are not familiar with the sudo command, see the
      Users and Groups guide.

      How to Use a Shebang in a Bash Script?

      The most common use of the Shebang is to specify the correct shell to use for a shell script. If a Shebang is not specified, the system uses the default interpreter belonging to the current shell. For example, in the Bash shell, the default interpreter is bash.

      To ensure the sh interpreter always processes a script, no matter what shell is active, a Shebang must be used. A Shebang such as #!/bin/sh or #!/usr/bin/env sh must be added. The system launches the sh interpreter, appending the name of the file as an argument. The interpreter treats the Shebang like a comment, which avoids an infinite loop, and interprets the remainder of the file.

      Using a Shebang with an Absolute Path

      One common method to use a Shebang is to specify the full path to the interpreter on the first line of the file.

      Note

      In this program, the line ps h -p $$ -o args="" prints out the name of the interpreter along with any arguments passed to it.

      To use a Shebang to define a mandatory interpreter for a shell script, follow these steps.

      1. Create a file named shebang_absolute with the following contents.

        File: shebang_absolute
        1
        2
        3
        4
        
        #!/bin/sh
        
        echo "Interpreter test. The interpreter and arguments are:"
        ps h -p $$ -o args=''
      2. Ensure the file is executable.

        chmod +x shebang_absolute
      3. Execute the file from the same directory. The sh interpreter is shown in the output.

        Interpreter test. The interpreter and arguments are:
        /bin/sh ./shebang_absolute
      4. Change the first line to #!/bin/bash and run the program again. The output now shows bash as the interpreter.

        Interpreter test. The interpreter and arguments are:
        /bin/bash ./shebang_absolute

      Using a Shebang with env

      For a more robust script implementation, use the env utility to determine the path to the interpreter. env uses the $PATH variable to search for the interpreter. It always returns the first match it finds.

      To use env in a Shebang, follow these steps.

      1. Create a new file named shebang_env. Add the following instructions.

        File: shebang_env
        1
        2
        3
        4
        
        #!/usr/bin/env sh
        
            echo "Interpreter test. The interpreter and arguments are:"
            ps h -p $$ -o args=''
      2. Change the file attributes so the file is executable.

      3. Execute the file. Run the command from the same directory as the new file.

        Interpreter test. The interpreter and arguments are:
        sh ./shebang_env

      Passing Options to the Interpreter

      A Shebang can pass through interpreter options. The directive #!/bin/sh -v runs the interpreter using the -v/verbose option. This option echoes each command to the screen upon execution. This example appends the -v option to the Shebang in shebang_absolute.

      #!/bin/bash -v
      
      echo "Interpreter test. The interpreter and arguments are:"
      Interpreter test. The interpreter and arguments are:
      ps h -p $$ -o args=''
      /bin/bash -v ./shebang_absolute

      Note

      If the Shebang uses env, do not declare the option within the Shebang. Instead, use the declaration set -v to set the option on the next line.

      How to Use a Shebang in a Python Script?

      In Python, the Shebang identifies which version of the Python interpreter to use. This feature might be necessary for older programs that cannot run on newer interpreters. Any script that requires Python version 2 can be redirected to the python2 interpreter. The Shebang #!/usr/bin/env python2 sets the Python interpreter to python2. Always use the env utility to set the path to the Python interpreter because it is sometimes installed in a non-standard directory.

      To use a Shebang with a Python script, follow these steps.

      1. Create the py_v3.py Python file. Add the following commands. The sys.version method displays the active version of the Python interpreter. Use import sys to import the necessary package.

        File: py_v3.py
        1
        2
        3
        4
        5
        
        #!/usr/bin/env python3
        
        import sys
        print("This version of Python is:")
        print(sys.version)
      2. Set the execute permission on the file.

      3. Run the executable file, but do not use the python3 command. The correct Python interpreter is selected at runtime based on the Shebang.

        This version of Python is:
        3.10.4 (main, Jun 29 2022, 12:14:53) [GCC 11.2.0]
      4. To confirm Python version 2 can be substituted in place of Python 3, create a new file py_v2.py and enter the following instructions.

        File: py_v2.py
        1
        2
        3
        4
        5
        
        #!/usr/bin/env python2
        
        import sys
        print("This version of Python is:")
        print(sys.version)
      5. Set the executable attribute and run the file. The program now displays information about the python2 interpreter.

        chmod +x py_v2.py
        ./py_v2.py
        This version of Python is:
        2.7.18 (default, Jul  1 2022, 10:30:50)
        [GCC 11.2.0]

      Overriding the Shebang Directive

      Even if a file contains a Shebang, it’s still possible to override it from the command line. One reason to do this might be to test how a script behaves with a different interpreter. From the command line, enter the name of the interpreter to use, followed by the name of the file. This tells the system to ignore the Shebang statement.

      In the following example, py_v2.py contains the Shebang directive #!/usr/bin/env python2. But if the command python3 ./py_v2.py is entered, the python3 interpreter is used instead.

      This version of Python is:
      3.10.4 (main, Jun 29 2022, 12:14:53) [GCC 11.2.0]

      Conclusion

      A Shebang indicates which Bash or Python interpreter to use to interpret an executable file. Shebangs are supported on Linux and many other operating systems. A Shebang begins with the characters #! and only occurs on the first line of the file. The interpreter can be specified using an absolute path or through the env program. It is possible to use a Shebang to pass additional parameters to the interpreter or to override a Shebang on the command line.

      More Information

      You may wish to consult the following resources for additional information
      on this topic. While these are provided in the hope that they will be
      useful, please note that we cannot vouch for the accuracy or timeliness of
      externally hosted materials.



      Source link

      How to Check Python Version


      Python reigns as one of the most popular programming languages, with a wide range of programs and developer tools relying on it. In fact, your system likely already has at least one version of Python installed.

      Many tools and Python development libraries require a particular version of Python. Thus, you may want to know where you can find information on your installed Python version. This can help you make decisions about compatibility, upgrades, and more.

      This tutorial shows you how to check your Python version, for both Python 2 and Python 3. Here, you can find the command line method as well as a Python script method for retrieving the current Python version.

      How to Check the Python Version from the Command Line

      The Python command comes with a command line option of --version that allows you to see your installed version.

      It works just as straightforwardly as it sounds. Enter the following command from your command line, and you should get an output similar to the one shown below:

      python --version
      
      Python 3.8.10

      Python 2 vs Python 3

      Some systems distinguish between Python 2 and Python 3 installations. In these cases, to check your version of Python 3, you need to use the command python3 instead of python.

      In fact, some systems use the python3 command even when they do not have Python 2 installed alongside Python 3. In these cases, you only have the python3 command.

      The command for checking the installed version of Python 3 remains otherwise the same – just use python3 with the --version option:

      python3 --version
      

      How to Check the Python Version from Python

      You can also check your installed Python version from within Python itself. Using either a script or the Python shell, you can use one of the code snippets below to print your Python version.

      Both options work equally well regardless of your system. The choice of which option to use really comes down to what format you want the output in.

      Using sys

      The sys module has a variable you can reference to get the current Python version. Below you can see an example of how the sys module’s version variable renders the current Python version. This code first imports the sys module then prints out the contents of the version variable:

      1
      2
      3
      
      import sys
      
      print(sys.version)
      
      3.8.10 (default, Jun 22 2022, 20:18:18)
      [GCC 9.4.0]

      As you can see, the sys.version variable contains more information about your installed Python version than just the number. For that reason, sys is a good module to turn to when you want more verbose version information.

      Using platform

      The platform module includes a function that fetches the current version of Python. The example code below uses this function to print the current Python version number. It first imports the platform module; then, the python_version function returns the version number to the print function:

      1
      2
      3
      
      import platform
      
      print(platform.python_version())
      
      3.8.10

      The output from the platform.python_version is more minimal compared to the sys module’s version variable. This makes the platform module more useful for cases when you only need the version number. For example, this method helps when you want to design a program to parse the Python version and act accordingly.

      Conclusion

      With that, you have everything you need for checking your current Python version. The steps above cover you whether you need to see the Python version from the command line or from within a Python script.

      You can continue learning about Python with our collection of
      Python guides. We cover everything from fundamental Python concepts to building Python web applications.

      Have more questions or want some help getting started? Feel free to reach out to our
      Support team.

      More Information

      You may wish to consult the following resources for additional information
      on this topic. While these are provided in the hope that they will be
      useful, please note that we cannot vouch for the accuracy or timeliness of
      externally hosted materials.



      Source link

      How to Learn Python (Fast & Free)


      There are plenty of resources available that can help you learn Python in no time. From free to paid options, you can find a wide selection of online courses and websites to guide you through the lessons. Using these resources, you can quickly progress from beginner to advanced.

      In this post, we’ll explain what Python is, what it’s used for, and why you might want to learn it. Then we’ll provide you with some of the top places you can go to learn Python as quickly as possible. Let’s jump in!

      An Introduction to Python

      Python is a versatile, high-level, object-oriented programming language that helps you solve problems quickly:

      The Python website

      To give you an idea of how sophisticated and practical this programming language is, consider that some of the biggest brands across the globe have used Python in their projects. These companies include Netflix, Google, and Spotify.

      It’s also a preferred language for many developers. Last year, RedMonk research found that, among developers, Python was the second most popular programming language (behind JavaScript).

      Python 2 and Python 3 are different versions of the open-source Python programming language. However, Python 2 is no longer supported by the Python community. Python 3 is the latest version and is recommended for all new projects.

      What Python Is Used For

      Python is used in many places, including:

      • Web development
      • Scientific computing
      • Data analysis
      • Artificial Intelligence (AI)
      • Machine learning
      • Automation and scripting
      • Software testing and prototyping

      You can also use Python to build all sorts of applications, including web, desktop, and mobile apps. One of the most common use cases for Python is web development, which is the process of building websites and applications.

      Web development can be divided into three parts: front-end development, back-end development, and full-stack development.

      Front-end developers focus on the User Interface (UI) and experience of a website or web app. They use HTML, CSS, and JavaScript to build the Graphical User Interface (GUI).

      Back-end developers focus on the server-side application that powers the front-end GUI. They use languages like Python to write code that runs on a web server. Finally, Full-stack developers are proficient in both front-end and back-end development.

      Get Content Delivered Straight to Your Inbox

      Subscribe to our blog and receive great content just like this delivered straight to your inbox.

      Why You May Want to Learn Python

      Python is a popular language for web development for many reasons. There are also a variety of benefits to learning it.

      For beginners, Python is relatively easy to learn and has powerful libraries for advanced users. It also has a simple syntax that is simple to read and understand. These features make Python an ideal language for beginners who are just getting started with coding.

      Additionally, the Python language is versatile enough for various purposes. This broad applicability makes it a good choice for developers who want to learn one language that they can use for multiple types of projects.

      It’s also fast. Python code is compiled to bytecode, which is then executed by the Python virtual machine. This compilation step means that Python code runs faster than interpreted languages like PHP and Ruby.

      Another benefit is that Python has powerful libraries that make web development easier. These libraries include Django, Flask, and Bottle. They provide helpful tools for building websites and web apps.

      For example, Django has a module called Django ORM that makes it easy to work with databases in Python. Furthermore, Flask provides a module called flask-restful that makes it easy to build REST APIs.

      Finally, since it’s such a popular programming language, Python also has a robust community to offer support and resources. This means that if you ever run into any Python-related issues or concerns, there will likely be an experienced developer capable of providing a solution.

      What to Learn Before Python

      Technically, you don’t need to know any other programming languages before learning Python. However, mastering different languages can make learning Python easier. If you’re just starting with web development, we recommend taking an introduction to programming course.

      At the very least, it’s best to have a solid grasp of HTML, JavaScript, and CSS. It might also be helpful if you understand the basics of other programming languages such as PHP and JavaScript libraries like React.

      There are two ways to use Python for web development: with or without a framework. A framework is a collection of libraries and tools that make it easier to build a website or web app.

      As we mentioned, the most popular Python frameworks for web development are Django, Flask, and Bottle. We recommend familiarizing yourself with one of these frameworks if you’re just starting.

      If you’re at least moderately experienced with Python, you may want to try developing without a framework. This approach is sometimes called micro-framing because you only use the libraries that you need for your specific project. This method can be faster and easier than using a full-fledged framework like Django or Flask.

      The time it takes to learn Python will depend on your experience level and how much effort you’re willing to invest. Overall, you can learn Python relatively quickly if you can dedicate a few hours each day.

      How to Learn Python Fast (5 Helpful Resources)

      Now that we’ve covered what Python is and its use cases, let’s discuss how you can go about learning it. Here are five helpful resources to get you started!

      1. The Python Website

      The official Python website offers many resources, guides, and tutorials that can introduce you to the basics of programming languages. If you’re starting from ground zero, we recommend the Beginner’s Guide, available under the Docs tab:

      The Python Beginner’s Guide

      This guide is free to access and use. It also provides tons of links to other materials you can utilize throughout your learning journey. In addition to what’s essentially a map for your Python curriculum, you can explore various quizzes and assignments, cheat sheets, style checkers, and other tools. We recommend taking notes to absorb all the information.

      Also available on the Python website is a Developer’s Guide. This resource will be helpful to reference once you’ve mastered the basics and are ready to move to the next level.

      2. Udemy

      Udemy is a popular platform where you can find tons of online learning courses covering a broad range of topics. The website offers both free and paid lessons, including options explicitly geared toward web developers.

      These classes include a free Introduction to Python Programming course that is perfect for beginners:

      The Udemy Intro to Python course

      It consists of one hour and 39 minutes of on-demand video content, covering the basics of Python, including scripts and functions. You can also upgrade to the paid version, which includes a certificate of completion and direct messaging with the instructor.

      When you’re ready to advance, you can enroll in the Python From Beginner to Intermediate in 30 Mins course. This is another free, video-based class that will teach you more sophisticated Python programming concepts.

      3. Codecademy

      Codecademy is a popular and robust online learning platform geared toward developers and programmers. It’s a wonderful resource for exploring and enrolling in classes that cover nearly every topic in data science, web development, IT, and more.

      Although it’s not free, the Pro plan offers a Learn Python 3 course that can serve as an excellent introduction to Python as well as basic programming concepts:

      Codecademy Learn Python 3

      The lessons cover a variety of topics, including:

      • Python syntax
      • Conditionals and control flow
      • Functions
      • Data structures lists and directories
      • And more

      The course doesn’t require any prerequisites. If you sign up for the Pro plan, you will receive a certificate upon completion. Furthermore, the course takes approximately 25 hours to complete.

      4. LearnPython.org

      If you prefer text-based learning materials, LearnPython.org is a solid option:

      The LearnPython.org website

      The website is dedicated to helping people of all experience levels learn the programming language and access resources that can simplify the process. It includes both basic and advanced tutorials, covering topics such as:

      • Variables and their types
      • Data science lessons
      • Generators, sets, list comprehensions, function arguments, etc

      The lessons are interactive. You can also find a Facebook group dedicated to the courses where you can discuss the material with other students.

      5. Free Code Camp

      Another platform you can use to find free and paid courses on Python is Free Code Camp. The website has various coding and web development materials, including courses, boot camps, and news.

      Free Code Camp offers a Learning Python: From Zero to Hero course that is free and text-based:

      Free Code Camp Python course

      It explains the basics of Python in simple, easy-to-understand sections. Some of the topics include:

      • How variables, conditional statements, and looping work
      • How to use lists
      • Iterations through data structures
      • Objects and classes

      If you enjoy video-based content, you can also find a YouTube version where the same topics are covered. The video course additionally discusses how to install PyCharm and Python. This course includes four hours and 20 minutes of video content.

      If you complete the beginner course and want to move on to more advanced concepts and projects, you can also participate in the One Month Python Bootcamp. This is a paid course, but the project-based, intensive material is self-paced. It will give you the foundation needed to become a Python developer.

      Start Learning Python Today

      If you’re just getting started with Python, there are many online courses, platforms, and resources you can use (many of which are free!) to help you learn the programming language quickly.

      We recommend beginning with a free introduction course or materials, such as those offered on Python.org. Once you nail down the basics, you can graduate to more in-depth and specialized teachings offered on third-party and premium platforms.

      Are you looking for an affordable yet reliable hosting solution for your web development projects? Check out DreamHost shared hosting plans to get started!

      Power Your Website with DreamHost

      We make sure your website is fast, secure and always up so your visitors trust you. Plans start at $1.99/mo.

      shared hosting



      Source link