How to Fix “subprocess-exited-with-error” in Python

If you’ve worked with Python for any significant length of time, you may have encountered a somewhat cryptic and frustrating error message: “subprocess-exited-with-error.” This error typically appears when installing packages using pip or building Python environments, and it leaves many developers scratching their heads.

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TL;DR

The “subprocess-exited-with-error” in Python usually occurs during package installation or execution via pip, when a required component or build process fails. Common causes include missing system dependencies, outdated pip or setuptools, and incompatible Python versions. You can usually fix it by updating tools, installing missing libraries, or using precompiled wheels. Understanding the context and reviewing the accompanying error message is key.

What Does “subprocess-exited-with-error” Actually Mean?

At its core, this error means that Python attempted to execute an external command via the subprocess module and it failed. This often occurs in the context of building a package that needs to compile components — such as C extensions — before installation.

Examples of when this error might arise include:

Installing packages that require compiling (e.g. cryptography, lxml, numpy).
Using pip to install from source and the compiler isn’t available.
Missing system libraries like libssl-dev or python3-dev.
Incompatibility between your Python version and the package you’re trying to install.

Step-by-Step: How to Fix the Error

1. Read the Full Error Message Carefully

This might sound obvious, but it’s the most important step. The subprocess-exited-with-error will usually be preceded or followed by logs that include precise module names, lines of failure, and missing dependencies. Look for messages like:


error: subprocess-exited-with-error

× Building wheel for cryptography (pyproject.toml) did not run successfully.

This type of output gives you a heads-up about the problem area — in this case, while building the cryptography module.

2. Update pip, setuptools, and wheel

Many build failures happen because your installation tools are outdated. Run the following command to make sure you have the latest versions:

python -m pip install --upgrade pip setuptools wheel

If you’re using a virtual environment (which is recommended), make sure you’re upgrading inside the environment.

3. Install System-Level Dependencies

Some packages depend on underlying operating system libraries or development headers. For example, to build cryptography, several Unix packages are needed. On Ubuntu, you can try the following:

sudo apt update
sudo apt install build-essential libssl-dev libffi-dev python3-dev

On Fedora or CentOS:

sudo dnf install gcc openssl-devel libffi-devel python3-devel

For Windows users, the process is different and may require installing build tools and MSVC components.

4. Try Installing a Precompiled Wheel

Python packages can be installed as either source distributions or binary wheels. Installing from source requires building tools, but wheels are pre-built. You can often install a wheel using:

pip install package-name --only-binary :all:

This tells pip to try fetching a binary version rather than building from source.

5. Create a Clean Virtual Environment

Sometimes your Python project environment becomes cluttered or misconfigured. Fixing the error might be as easy as restarting with a fresh environment:

python -m venv new-env
source new-env/bin/activate  # On Windows use: new-env\Scripts\activate

Then, try running your installation again within this clean space.

6. Use Compatibility Tags and Correct Python Version

Ensure the package is compatible with your Python version. Check the Python version the package supports on its PyPI page or documentation. If you’re using Python 3.11 and the package only supports up to 3.10, you may need to downgrade Python or look for an alternative package maintained for your version.

7. Use Logs to Debug the Compilation Step

If you’re not sure what’s going wrong, you can pipe debug output to a file using:

pip install package-name -v > pip-debug.log 2>&1

This will create a pip-debug.log file capturing all output, which can help you or others on StackOverflow pinpoint the exact problem.

A Real Example: Installing Cryptography

Cryptography is one of the most commonly used Python libraries that causes build errors. Here’s a breakdown of how to solve it:

Start by updating pip and build tools:

pip install --upgrade pip setuptools wheel

Install required OS packages (Ubuntu):

sudo apt install build-essential libssl-dev libffi-dev python3-dev

Then try:
```
pip install cryptography
```

If you’re on Windows, consider using a wheel from Gohlke’s unofficial binaries and install it like this:

pip install path_to_downloaded_wheel.whl

Additional Tips

Use Docker or containers: If you’re struggling with package builds on your machine, consider using Docker where you can control the system environment.
Look at Pyproject.toml: For packages that use Modern Python build systems, the pyproject.toml file contains information on build dependencies. Make sure required fields are fulfilled before building.
Avoid Alpha/Beta Python versions: Using Python nightly or beta versions may result in compatibility issues with many popular packages.

Common Packages Known to Cause This Error

Here are some packages that frequently trigger the “subprocess-exited-with-error” message, mostly because they require compilation steps:

cryptography – Requires OpenSSL and C libraries
lxml – Needs libxml2 and libxslt headers
numpy – On some platforms, building from source without a wheel can fail
pandas – Very reliant on C extensions, especially during early builds or custom pip installs

Final Thoughts

While the “subprocess-exited-with-error” might seem daunting at first glance, it’s often just a sign that something didn’t go according to plan during an installation process. More often than not, the cause is resolvable with the right package versions, system dependencies, or environment setups.

The key to overcoming it is to stay calm, carefully analyze the full traceback, and proceed with methodical troubleshooting. Whether you’re a beginner or an experienced Pythonista, these tricks should help you move past the roadblock quickly and efficiently.

Happy coding!