How to Run Python Script on the Command Line

If you are interested in taking your Python skills to the next level, learning how to run python script from the command line is a must.

The command line can be a powerful tool on its own, and being able to run Python scripts from the command line can streamline your workflow, automate repetitive tasks, and make it easier to collaborate with others.

In this tutorial, we will cover the basics of running Python scripts from the command line and provide tips and best practices along the way.

Whether you are new to python programming or have some experience under your belt, this tutorial has something for you. Let’s dive in!

Why running Python Script from the command line is powerful

Running python script from the command line is powerful because it allows you to use and combine a wide range of software and packages that have been developed and shared by the community, and to automate processes and tasks that would be time-consuming or inconvenient to do manually.

Here are a few examples of what you can do with python script when run from the command line:

You can use command line arguments to pass input data to your python script, and use flags to customize its behavior.

For example, you could write a script that processes a batch of images and use a command line flag to specify the input and output directories.

You can use shell commands and pipes to chain together multiple processes and create complex workflows.

For example, you could use a python script to download a large dataset from the internet, extract the data, and then use another script to process and analyze the data.

You can use the script as a utility to perform common tasks, such as renaming files in a directory, generating reports, or automating deployments.
You can use the script as a standalone application or as a library that can be called from other scripts or programs.

Overall, running Python scripts from the command line gives you a lot of flexibility and can make your workflow more efficient and easier to automate.

Introduction to the command line: A brief overview

The command line is a text-based interface for interacting with a computer’s operating system and other software.

It allows users to enter commands, which are then executed by the system and can be used to perform a wide variety of tasks. The command line is often preferred by developers and advanced users because it provides a direct and powerful way to access and control the system.

To use the command line, users open a terminal window or command prompt and type in commands.

The command line interpreter then processes the command and produces an output, which can be text or some other form of data.

Here are a few examples of common command line commands:

ls – List the files and directories in the current directory.
cd – Change the current working directory.
mkdir – Create a new directory.
touch – Create a new file.
rm – Remove a file or directory.

In addition to running commands, the command line also supports various operations such as input/output redirection, piping, and script execution. These features can be used to create complex workflows and automate tasks.

For example, you can use the grep command to search for a pattern in a text file and the wccommand to count the number of lines, words, and characters in a file:

grep "Roland" input.py

This searches for the word “Roland” in a python file with the name “input.py“

You can also use the | character to pipe the output of one command as the input to another command:

ls | wc -l

This would count the number of files and directories in the current directory.

You can equally use the ./ prefix to run a python script from the command line.

For example, if you have a Python script called myscript.py, you can run it with the following command:

./myscript.py

The ./ tells the system to look for the script in the current directory (i.e., “./”) rather than searching the system’s PATH for the script.

This will run the script myscript.py in the current directory.

Keep in mind that the script must have the correct permissions for execution.

You can use the chmod command to change the permission of a script:

chmod u+x myscript.py

This makes the script executable.

Setting up your python environment

To set up your Python environment, you need to install a Python interpreter and any necessary libraries and packages.

Here are the steps you can follow to set up your python environment:

Install python: you can download and install python from the official python website https://www.python.org/downloads/. Make sure to choose the version that is appropriate for your system (e.g., 32-bit or 64-bit).
Verify the installation: to verify that python has been installed correctly, open a terminal window and type the following command:

python --version

This will print the version of Python that is installed on your system.

For a more detailed explanation of how to Install Python, be sure to check out our previous post – How to Quickly Install Python on Windows 10

That’s it! Your Python environment is now set up and ready to use. You can start writing and running Python scripts.

Writing your python script

To write a python script, you can use any text editor that can handle plain text files.

Some popular options include Notepad (on windows), vi or vim (on Unix / Linux), and TextEdit (on macOS).

Keep in mind that a Python script is just a text file, so you can also write and edit your script using a code editor like Visual Studio Code or PyCharm. These tools often include additional features like syntax highlighting and code completion to make writing and debugging code easier.

Here is a step-by-step guide to writing a simple Python script:

Open your text editor and create a new file
Type your Python code into the file
Use clear and descriptive variable names. This will make your code easier to read and understand.
Use comments to explain what your code is doing. This will help others (and your future self) understand your code.
Use white space to improve the readability of your code. This includes using blank lines to separate blocks of code and indenting to show the structure of your program.
Save the file with a .py extension. This tells the computer that the file is a python script
Use a good coding style. Pycodestyle (formerly called pep8) is a style guide for Python that provides guidelines for writing clean, readable code.
Test your code thoroughly. This will help you catch bugs and ensure that your code is working as expected.

Here is an example of a simple Python script:

# Set the initial sum to 0
sum = 0
# Add the first 10 positive integers
for i in range(1, 11):
  sum += i
# Print the result
print("The sum of the first 10 positive integers is", sum)

To run this python script, save it as a .py file and run it using the python command in a terminal or command prompt.

Output
The sum of the first 10 positive integers is 55

Navigating to the directory of your script

To run the python script above, you need to navigate to the directory where you saved it.

To navigate to the directory where your script is saved, open your command prompt or terminal and use the cd (change directory) command.

For example, if your script is saved in a directory called my_scripts on your desktop, you can navigate to that directory by using the following command:

cd Desktop/my_scripts

Note: The directory structure on your computer may be different, so you will need to modify the path to reflect the location of your script.

Running your python script from the command line

Once you have navigated to the correct directory, you can run your script by typing python script.py where “script.py” is the name of your script.

python script.py

When you run the script, it will calculate and print the sum of the first 10 positive integers (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 = 55).

Congratulations on successfully running your python script from the command line! This is a great accomplishment, and you should be proud of your hard work and dedication.

Common errors when running python script and how to troubleshoot them

There are several common errors that you may encounter when running a python script from the command line.

Here are a few of the most common ones, along with some suggestions for how to troubleshoot them:

“python: command not found”: This error means that the Python interpreter is not installed on your system, or it is not in your system’s PATH. To fix this, make sure that Python is installed, and try adding the directory where Python is installed to your PATH, or you can specify the full path to the Python interpreter when running the script (e.g., /usr/bin/python3)

“syntaxError: invalid syntax”: This error means that there is a syntax error in your code. Check the line of code where the error occurred, and make sure that you have written it correctly. Make sure that you are using proper indentation, and that you have closed any brackets or quotes that you have opened.
“NameError: name ‘x’ is not defined”: This error means that you are trying to use a variable that has not been defined. Make sure that you have defined the variable before your try to use it, or check that you have spelled the variable name correctly.
“TypeError: unsupported operand type(s) for +: ‘int’ and ‘str’”: This error means that you are trying to perform an operation on incompatible types. Make sure that you are using the correct types for the operation you are trying to perform. For example, you cannot concatenate a string and an integer using the + operator.
“ImportError: No module named ‘x’”: This error means that you are trying to import a module that is not installed on your system. Make sure that you have installed the module, or check that you have spelled the module name correctly.

I hope this helps! If you encounter any other errors when running your python script, feel free to ask for help here. I will do my best to assist you in troubleshooting the problem.

Conclusion

Congratulations on taking the first steps towards mastering the command line and running python scripts! This is an important skill for any programmer to have, and with a little practice and persistence, you will be well on you way to becoming proficient at it

Using the command line can seem intimidating at first, but with time and experience, you will find it to be a powerful and efficient tool for running your Python script. You will be able to automate tasks, process data, and build command line applications that can be used by other people.

So don’t be afraid to dive in and start experimenting with the command line. With a little bit of practice, you will be a pro in no time! Keep learning and working hard. Soon you will be able to run Python scripts from the command line with ease.

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