How to Fix the No module named 'pytest' Error in Python 3.9 with Miniconda

Solve the 'No module named pytest' error in Python 3.9 on Ubuntu 18.04 with Miniconda. Learn how to correctly install pytest in your conda environment.
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Troubleshooting the 'No module named pytest' Error with Python 3.9 and Miniconda

If you've recently installed Miniconda along with Python 3.9 on your Ubuntu 18.04 system, you might be encountering a frustrating issue when trying to import pytest. The error message "No module named 'pytest'" is a common headache for many developers. In this guide, we will dive into the problem and provide a clear, step-by-step solution.

Understanding the Problem

After installing pytest, you might have verified its installation using the command:

[[See Video to Reveal this Text or Code Snippet]]

And received the output:

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However, when you try to run Python and import pytest, you see the following error:

[[See Video to Reveal this Text or Code Snippet]]

This is confusing! You can see that pytest seems to be installed, yet Python cannot find it. What could be going wrong?

The Source of the Problem

The core of this issue lies in how Python environments work with Conda. Even though pytest is installed, it's not in the environment that Python is using to run your scripts. In the output, /usr/bin/pytest indicates that pytest was installed via your system’s package manager rather than through Conda.

Why Does This Matter?

When you create a Conda environment, it uses its own isolated installation of Python and packages, separate from the system-wide installations. If you've installed pytest through the system level and not in your Conda environment, Python will not be able to locate it when you try to import it. This is why you're seeing the error message.

The Solution: Installing pytest through Conda

To resolve this issue, you need to install pytest in your current Conda environment. Follow these simple steps:

Open your terminal.

Activate your Conda environment (if you have not already done so). You can activate it using:

[[See Video to Reveal this Text or Code Snippet]]

Replace your-env-name with the name of the environment you want to work in.

Install pytest via Conda using the following command:

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This command specifies using the conda-forge channel, which is known for having a comprehensive range of packages and their most updated versions.

Verify the installation by running:

[[See Video to Reveal this Text or Code Snippet]]

You should see a path that resembles something like /home/your-user-name/miniconda3/envs/your-env-name/bin/pytest, confirming that pytest is now installed within your Conda environment.

Now, run Python again and attempt to import pytest:

[[See Video to Reveal this Text or Code Snippet]]

If no errors appear, congratulations! You've successfully resolved the issue.

Conclusion

Resolving the "No module named 'pytest'" error is straightforward once you understand the relationship between your Python installations and Conda environments. Always ensure that you install the necessary packages in the respective environment you are working with to avoid module not found errors.

If you have any additional questions or run into other Python-related issues, feel free to explore further resources or ask for help in community forums. Happy coding!